Compute each sum or difference

9/10+7/9

1/2-3/11

2/5-1/15

Step-by-step explanation:

1) 9/10+7/9

The first step is to take the lowest common factor of 10 and 9 in the denominator. It is 90. Therefore,

9/10+7/9 = (9 * 9 + 7 * 10) / 90 =

(81 + 70) / 90 = 151/90 = 1 61/90

2) 1/2-3/11

The first step is to take the lowest common factor of 2 and 11 in the denominator. It is 22. Therefore,

1/2-3/11 = (11 - 6) / 22 = 5/22

3) 2/5-1/15

The first step is to take the lowest common factor of 5 and 15 in the denominator. It is 15. Therefore,

2/5-1/15 = (6 - 1) / 15 = 5/15 = 1/3

1. 9/10 + 7/9 = 81/90 + 70/90 = 151/90 = 1 61/90

2. 1/2-3/11 = 11/22-6/22 = 5/22

3. 2/5-1/15 = 6/15-1/15 = 5/15 = 1/3