Direction In each series, look for the degree and direction of change between the numbers. In other words, do the numbers increase or decrease, and by how much-
21.

28 25 5 21 18 5 14
A. 11 5
 B. 10 7
C. 11 8
 D. 5 10
Answer and Explanation
Answer: A

Explanation: This is an alternating subtraction series with the interpolation of a random number, 5, as every third number. In the subtraction series, 3 is subtracted, then 4, then 3, and so on.




22.

8 11 21 15 18 21 22
A. 25 18
 B. 25 21
C. 25 29
 D. 24 21
Answer and Explanation
Answer: B

Explanation: This is an alternating addition series, with a random number, 21, interpolated as every third number. The addition series alternates between adding 3 and adding 4. The number 21 appears after each number arrived at by adding 3.




23.

9 16 23 30 37 44 51
A. 59 66
 B. 56 62
C. 58 66
 D. 58 65
Answer and Explanation
Answer: D

Explanation: Here is a simple addition series, which begins with 9 and adds 7.




24.

2 8 14 20 26 32 38
A. 2 46
 B. 44 50
C. 42 48
 D. 40 42
Answer and Explanation
Answer: B

Explanation: This is a simple addition series, which begins with 2 and adds 6.




25.

9 11 33 13 15 33 17
A. 19 33
 B. 33 35
C. 33 19
 D. 15 33
Answer and Explanation
Answer: A

Explanation: In this alternating repetition series, a random number, 33, is interpolated every third number into a simple addition series, in which each number increases by 2.