1. 21, 25, 18, 29, 33, 18, ... choose which pair of numbers comes next?

a) 43, 18

b) 41, 44

c) 37, 18

d) 37, 41

Explanation: This is a simple addition series with a random number, 18, interpolated as every third number. In the series, 4 is added to each number except 18, to arrive at the next number.

2. 75, 65, 85, 55, 45, 85, 35, ... choose which pair of numbers comes next?

a) 25, 15

b) 25, 85

c) 35, 25

d) 85, 35

Explanation: This is a simple subtraction series in which a random number, 85, is interpolated as every third number. In the subtraction series, 10 is subtracted from each number to arrive at the next.

3. 11, 16, 21, 26, 31, 36, 41, ... choose which pair of numbers comes next?

a) 47, 52

b) 46, 52

c) 45, 49

d) 46, 51

Explanation: In this simple addition series, each number is 5 more than the previous number.

4. 3, 8, 13, 18, 23, 28, 33, ... choose which pair of numbers comes next?

a) 39, 44

b) 38, 44

c) 38, 43

d) 37, 42

Explanation: In this simple addition series, each number is 5 greater than the previous number.

5. 84, 78, 72, 66, 60, 54, 48, ... choose which pair of numbers comes next?

a) 44, 34

b) 42, 36

c) 42, 32

d) 40, 34

Explanation: In this simple subtraction series, each number is 6 less than the previous number.

6. 5.2, 4.8, 4.4, 4, ... What number should come next?

a) 3

b) 3.3

c) 3.5

d) 3.6

Explanation: In this simple subtraction series, each number decreases by 0.4.

7. 8, 6, 9, 23, 87 , ... What number should come next?

a) 128

b) 226

c) 324

d) 429

Explanation: 8 x 1 - 2 = 6

6 x 2 - 3 = 9

9 x 3 - 4 = 23

23 x 4 - 5 = 87

87 x 5 - 6 = 429 ...

8. 28, 25, 5, 21, 18, 5, 14, ... choose which pair of numbers comes next?

a) 11, 5

b) 10, 7

c) 11, 8

d) 5, 10

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.

9. 8, 11, 21, 15, 18, 21, 22, ... choose which pair of numbers comes next?

a) 25, 18

b) 25, 21

c) 25, 29

d) 24, 21

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.

10. 9, 16, 23, 30, 37, 44, 51, ... choose which pair of numbers comes next?

a) 59, 66

b) 56, 62

c) 58, 66

d) 58, 65

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