Which is a good comparison of the estimated sum and the actual sum of 7 9/12+2 11/12

7 9/12 = 7.75

2 11/12 = 2.917

So we ca round both of these up.

7.75 rounds to 8

2.917 rounds to 3

8 + 3 = 11

So the estimated sun is 11.

7 9/12 + 2 11/12 = 10 2/3

So the actual sum is 10 2/3.

The estimated sum is a pretty good estimate to the original number.