Question

1) Which of the following arithmetic sequences have a common difference of 2 1/2?

A) -4,-1.5,1,3.5,6,8.5
B) 2 1/2, 4 1/2, 6 1/2, 8 1/2, 10 1/2
C) 1.5,3,4.5,6,7.5
D) -5, -3 1/2, -1 1/2, 2

2) In this arithmetic sequence, what is the common difference?

11, 8, 5, 2, ...

3
-3
5
-1

Answer 1

Answers:
1) A
2) -3

Work:
1) The answer is A because there is a common difference of 2.5 between each term, meaning that exactly 2.5 is added between each successive term of the sequence. 
2) The answer is -3 because in order to get from one term to the next in the above sequence, you must subtract 3. For instance, 11-3=8, 8-3=5, and so on. Since you are subtracting the value must be negative, giving you -3.