Which of the following would be a good estimate for -7.94-2.31? a. -9 b. -5 c. -6 d. -10

A good estimate would be -10.

In order to estimate, start off by rounding both numbers to the nearest whole number. -7.94 can be rounded to -8 because the first number to the right of 7 is greater than 5. 2.31 can be rounded to 2 because the first number to the right of the 2 is less than 5. 

After rounding, the expression becomes -8-2, which is equal to -10.

Iwould say they are complementary because that’s the division of a 90 degree angle and it’s split between the middle of them