Subtracting Mixed Numbers with Different Denominators and Borrowing

You can add only fractions together that have the same dennominator, so you must first change each of the two fractions to a common denominator.

Example 1 Suppose you have two mixed numbers 3 1/4 and 1 2/3 to be subtracted

3	1		1	2
	---	-		---	=		---
	4			3

First you must find common denominators.

Select the denominator of the second fraction (4) and multiply the first fraction (1/3) by that number:

2		4		8
---	x	---	=	---
3		4		12

Select the denominator of the first fraction (3) and multiply the second fraction (1/4) by that number:

1		3		3
---	x	---	=	---
4		3		12

These two fractions (8/12 and 3/12) have common denominators.

The two fractions cannot be subtracted as written. You will need to borrow.

Add the two new fractions together:

4		3		7
---	+	---	=	---
12		12		12

So your answer will be

1	4		3	3		4	7
	---	+		---	=		---
	12			12			12