# Hot Math How-Tos

### How To: Solve reverse percentage problems

We know the method for answering the question "What is the x percent of y" but, what about the answer to the following question "The x percent discounted price of an article is y. Find the original price." This is a reverse percentage problem that can be solved using the method shown in this video. This video contains three reverse percentage problems. The first two problems are essentially of the same type as explained above. A simple and easy to understand method of finding the original pri...

### How To: Increase or decrease by a percentage

In this video, we learn how to increase or decrease by a percentage. First, to increase you will need to find what the percent of the number is. To do this, you will find 10%, which should be very easy. As soon as you've found this, you can add or subtract to find the percent you need. Then, add this onto the original number and you'll know the percentage. To decrease the percentage, you will do the same type of equation. Except, you will need to subtract as you go to finish the problem. When...

### How To: Evaluate functions by substituting in the variable to the input given

In this video, we learn how to evaluate functions. When evaluating functions, you substitute in the variable to the input given. Once you do this, you will rewrite the equation filing in the appropriate spots with the numbers that you are given. After this, you will evaluate the equation with the proper steps in math. Once you have figured out the problem, you can do this in reverse to make sure you have the correct answer. This is a very easy process and it doesn't take that long. Just make ...

### How To: Divide and give an answer as a fraction

In this video we learn how to divide and give an answer as a fraction. If you are starting out with a simple fraction, you will simply take the number before the divide sign on the top and the second number on the bottom. If you end up with a number that is able to be simplified, make sure you take it down to it's most simple version possible. You can end up with a top heavy fraction, which means there will be whole numbers involved. Do the division to figure out how many times the bottom num...

### How To: Simplify complex rational expressions

In order to simplify complex rational expressions, it is important to be able to find the lowest common denominator. Complex rational expressions are fractions that are divided by fractions. When you have found the lowest common denominator, then, you should multiply both fractions by the common denominator.

### How To: "Back out the tax" from a receipt

In this video, we learn how to back out the tax from a receipt. If you have a receipt where you see how much you paid and know the tax rate, except you want to figure out the cost of the item before the tax. First, take the cost of the item including tax and what the tax rate is. To figure out the original price, let x equal the cost of the item. Add the tax to the cost of the item which will equal the cost you paid. Perform the equation 1x+(tax rate)= (total price). After you figure this equ...

### How To: Solve permutation & combination word problems

From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test). With this installment from Internet pedagogical superstar Salman Khan's series of free math tutorials, you'll learn how to unpack and solve word problems invplving permutations and combinations in basic stati...

### How To: Solve rational expression simplification word problems

From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test). With this installment from Internet pedagogical superstar Salman Khan's series of free math tutorials, you'll learn how to unpack and solve word problems that require you to simplify rational expressions.

### How To: Express inequalities using interval notation

With all the subjects offered in junior high and high school, math isn't a favorite for many. It can often times be confusing and although the results are concrete and don't require anybody to be imaginative, it can still pose a problem. In this tutorial, you'll find out how to express inequalities using interval notation. Good luck and enjoy!

### How To: Simplify expressions involving absolute value

Need to know how to simplify expressions involving absolute values? It's an absolute cinch. Learn how with this free video lesson. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test). With this free math tutorial, you'll learn how to divide one fraction into an...

### How To: Solve equations with the order of operations

In mathematics, the order of operations define the priority in which complex equations are solved. The top priority is your parenthesis, then exponents, followed by multiplication and division, and finally addition and subtraction (PEMDAS). This video tutorial demonstrates the order of operation with various examples and explains the associated methodology. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autod...

### How To: Factor trinomials with the "bottoms up" method

After an easy way to factor trinomials in algebra? Try the bottoms up method! Learn how with this free video lesson. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test).

### How To: Figure out the domain & range of a piecewise function

Need to calculate the domain and range of a graphed piecewise function? Learn how with this free video lesson. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test).

### How To: Calculate the height and volume of a pyramid

Need to know how to calculate the height and volume of a pyramid in geometry? Learn how with this free video lesson. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test).

### How To: Solve a 2x2 system of linear equations with inverses

See how to solve a two-by-two system of linear equations using inverses (derived from determinants). Learn how with this free video lesson. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test).

### How To: Use an asymptote to find the equation of a hyperbola

Need instruction on how to find the equation of a hyperbola using an asymptote? Learn how with this free video lesson. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test).

### How To: Clear fractions from linear equations in Algebra

Need help figuring out how to remove fractions from linear equations in algebra? Learn how with this free video lesson. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test).

### How To: Prove Rank(A) = Rank(transpose of A) in linear algebra

Learn how to prove that the rank of a matrix, A, is equal to the rank of its transpose in linear algebra. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test).

### How To: Solve word problems involving age in algebra

Need to know how to solve algebraic word problems involving age? From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test). With this three-part installment from Internet pedagogical superstar Salman Khan's series of free math tutorials, you'll learn how to unpack an...

### How To: Find the median & inter-quartile range

This video shows us the method to find the median and the inter-quartile range. The first step involves the arrangement of the numbers in the ascending order. Median is the middle number. The middle number is the number at (number of numbers + 1)/2 if the number of numbers is odd or the (number of number)/2 if the number of numbers is even. In the example the number is located at [(11+1)/2] or the 6th number. The inter-quartile range is higher quartile - lower quartile. The higher quartile is...

### How To: Work out the area of a triangle and a parallelogram

This tutorial describes the method to calculate the area of a triangle and a parallelogram To calculate the area of a triangle:

### How To: Solve a word problem that involves proportions

In this Education video tutorial you will learn how to solve a word problem that involves proportions. To solve such problems you got to express the scenario in proportions. For example, in the problem, ‘Jacob ran 10 miles in 80 minutes’; this rate can be expressed as 10miles/ 80 minutes. The second part of the problem is to find out ‘at that rate how far would he run in 2.5 hours’? ‘How far’ being a variable, write it as ‘x’ and this can be expressed as x/ 2.5 hours. So, the complete equatio...

### How To: Simplify exponential expressions in basic algebra

The video shows how to solved mixed property problems using the exponent rules. See if there are any rules you can apply to the problem until you get to a point where you can't simplify anymore. The instructor shows in the example problem that the two bases are the same, but there is extras happening the numerator. The power to power multiply rule is applied removing the extra issues from the numerator. Next the quotient rules is applied as there is the exact same base to the power so we keep...

### How To: Find least common multiple in rational expressions

This series walks you through the steps of finding the least common multiple in rational expressions. This excellent video shows you a clean board, with the instructors voice showing exactly what to do. Don't fret, any question you may have, will be answered. Watching this video will make you feel like your back in the classroom but rather comfortably from your home.

### How To: Figure out a tip without a calculator

To figure out a tip without a calculator, first remove the pennies amount in the bill. For example, if your bill is \$23.76 becomes \$23.70. To figure out a 10% tip, move the decimal point one place to the left. So, 23.70 becomes 2.370 or \$2.37. Bump up that number to \$2.30 or \$2.40 or \$2.50 cents, depending on your preference. Since 20% equals two times 10%, double the figure you computed for 10%. So, \$2.30 becomes \$4.60, or \$2.40 becomes \$4.80 or \$2.50 becomes \$5.00. Using this method, you wo...

### How To: Simplify complex fraction w/ single fraction on bottom

This is a great instructional video on education. This educational video teaches you how to simplify a complex fraction with a single fraction on bottom. Let us learn this with an example. Let us assume we have to simplify the complex fraction 5 by x-4 divided by 5-4x by 5. When you simplify this you will get 5-4x over x divided by 5-4x over 5. You will now get 5-4x over x multiplied by 5 over 5-4x. This is equal to 5 over x. This is how we have to simplify a complex fraction with a single fr...

### How To: Convert from cubic yards to cubic feet and inches

brettman6533 teaches you how to convert from cubic yards to cubic feet and inches. The volume of a cube is side cubed. If the side of a cube is 1 foot, then the volume would be 1 foot squared. Knowing that a foot equals 12 inches, you transform that into 1 times 12 in times 12 in times 12, which equals 1728 inches squared. If you want to convert a cubic yard, you have to remember 1 yard equals 3 feet. So now 1 yard squared is 1 times 3 feet times 3 feet times 3 feet, which is 27 feet squared....

### How To: Find the percent change using proportions

In this video, the instructor shows how to identify the percentage change using proportions. When a given quantity increases or decreases by certain amount then we can calculate the percentage change in the quantity, which can be either increase or decrease based on the new value of the quantity. To solve these kind of situations you should know that the ratio of amount of increase (or decrease) of an amount to its original amount is equal to the ratio of percentage increase (or decrease) to ...

### How To: Solving for "x" using addition and subtraction

The first operations you will need to know when learning to use algebra to solve for an unknown variable “x” will be using addition and subtraction. You can check you work by checking the balance of the equation when you are done.

### How To: Solve linear absolute value equations & inequalities

In this video the instructor shows how to solve linear absolute value equations and inequalities. You need to remember basic rules to solve these kind of problems. When the absolute value is equal to a number then the real value of it is equal to either the positive value of that number or negative value of that number. In case the absolute value is less than or equal to a number, then the real value lies in between the positive and negative values of that number. In the third case, if the ab...

### How To: Find the formula of a piecewise function given a graph

This video shows how to find the formula of a piecewise function when given a graph. The first step is to write a definition for the graph, which is done by identifying the different domains shown in the graph. The second step is writing formulas for each domain specified by the lines in the graph. The point-slope formula is used to identify the slope and y-intercept for the leftmost domain, which has a sloped line. A point and horizontal line make for simpler equations in the other pieces of...

### How To: Factor and collect like terms

In this video, the instructor shows how to collect like terms and factorize. When you are given a linear equation, the first thing you do is to try to organize it. Pair up the like terms. Add the numerical coefficients of terms with the same variables. This is called collecting the like terms. In case you see any common factor across all the terms, pull it out and tag it to the parenthesis. In this way, you can factorize the equation. Next, bunch together your like terms and sum them up. The ...

### How To: Solve percent equations

In this tutorial the instructor shows how to solve percent equations. The general form of a percent equations is that a is b% of c. As there can be three kinds of variables a, b, c, the questions involving percent equations can be of three types having one of the three variables unknown. These kind of percent statements can be solved easily by setting up an equation. So, to convert percent statement into a equation replace the unknown term with n, the 'is' term with equals sign and the '%' si...

### How To: Do long division without a calculator

This video shows you step by step how to do long division without the use of a calculator. The video shows viewers two different ways to solve a division problem. It first shows how to do the problem the traditional way, then it shows how to do it according to the long division process. The long division process is where you write the whole division, multiplication, and subtraction process out showing all your work. Long division is mainly used when dividing large numbers. There are three com...

### How To: Graph half an ellipse

If you are given an equation of ellipse in the form of a function whose value is a square root, you may need to simplify it to make it look like the equation of an ellipse. Now equate the function to a variable y and perform squaring on both sides to remove the radical. Now simplify the equation and get it in the form of (x*x)/(a*a) + (y*y)/(b*b) = 1 which is the general form of an ellipse. Now you will have the x and y intercepts which are a and b respectively. Using this values graph the eq...

### How To: Find the circumference of a circle

Use a simple mathematical formula to find the circumference of a circle. The circumference of a circle can be determined by using the formula 2 times pi times the circle's radius. Pi is equal to 3.14. If a circle's radius is 10 centimeters, first multiply pi times 2. Pi, or 3.14, times 2 is 6.28. The next step then is to multiply 6.28 times the circle's radius. Since the circle's radius is 10 centimeters, multiply it by 6.28. This gives you 60.28. 60.28 inches, then, is the circumference of t...

### How To: Convert percents into fractions and decimals

This video shows you how to convert percents to fractions and decimals To convert percent to decimal or fraction it is important that we know the meaning of percent which is per 100. So to convert a percent to fraction is simply to put in over 100 and simplify. Now to convert percent to decimal is to move the decimal point two spots to the left. if you don't see a decimal point, it is understood that is behind the last digit of the number.

### How To: Find the sum of reciprocals of complex numbers

In this tutorial the instructor shows how to calculate the sum of reciprocals of complex numbers. If you have to find out the sum of the reciprocals of two complex numbers first you will have to find out the least common multiple of the denominators. To do this multiply the numerator and denominator of the first fraction by the second complex number. Similarly multiply the numerator and denominator of the second fraction by the first complex number. Now you will have two fractions whose denom...

### How To: Evaluate logarithms using a calculator TI-83

A video to help calculator users find the natural logarithm (log base e, or "ln") and standard logarithm (log base 10, or simply "log") of any number using a TI-83 calculator (works for any issue of the TI-83 calculator or even a TI-84 calculator). Turn on your calculator. To find the natural log of a number, press the "ln" button (the third button from the bottom left), enter the number you want to find the natural log of, press the ")" (closed parenthesis) button, then press enter. The same...

### How To: Do algebraic long division

In this video, you can learn how to do algebraic long division. Take an easy example, such as 88 divided by 4. You are actually dividing 4 into 88. You take the 4 and divide it into the 80, and your answer is 20. Multiply (20 x 4) and you get 80, then subtract the 80 from 88 and you get 8. You then divide 4 into the remaining 8 and your answer is 2, giving you a final answer of 22. Try a harder problem, such as 2105 divided by 12. You are dividing 12 into 2105. The easiest way to handle this ...