Question

Form a sequence that has two arithmetic means between -13 and 89.

Answer 1

It would be D. If you add all the numbers (-18, -81, 144) and divide it by 3 then you would get -81. I hope I helped!

Answer 2

Compare the problem statement to the answer choices. (Check the offered answers.) Only the first two sequences start with -13 and end with 89, so selections (b) and (d) can be rejected. The differences between terms of sequence (a) are not constant, so it is not an arithmetic seqence. That only leaves ...
  c. -13, 21, 55, 89