This video teaches you to subtract mixed numbers with borrowing. Consider 2 mixed numbers. For example 8 and 2/7 and the other 5 and 4/5.You have to subtract 5 and 4/5 from 8 and 2/7. First you have to convert the fractions to their common denominator. To equate the denominators of these two fractions you have to multiply the first denominator with the numerator and the denominator of the second fraction and also multiply the numerator and denominator of the first fraction with the denominator of the second. In this case you have to multiply 2*5/7*5 which is equal to 10/35 and 4*7/5*7 which is equal to 28/35.Now we have the mixed fractions as 8 and 10/35 and the other is 5 and 28/35.Now you know you cannot subtract 28 from 10.So you have to borrow 1 from 8 so now 8 becomes 7. Then the 1 that is borrowed is used to increase the numerator of the first fraction.1 is multiplied with the denominator 35 and then is added to the numerator 10 so now the fraction is 45/35 and now the first mixed number is 7 and 45/35. Now it will be appropriate to subtract 5 and 28/35 from 7 and 45/35. So when you subtract the whole numbers 7-5 you get 2 and then the fractions 45/35 - 28/35 you get 17/35. the whole answer is 2 and 17/35.