# Number Series

Look carefully for the pattern, and then choose which pair of numbers comes next.

10 20 25 35 40 50 55

**Answer**: (e)

**Explanation:**

This is an alternating addition series, in which 10 is added, then 5, then 10, and so on.

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1 10 7 20 13 30 19

**Answer**: (c)

**Explanation:**

Here, every other number follows a different pattern. In the first series, 6 is added to each number to arrive at the next. In the second series, 10 is added to each number to arrive at the next.

40 40 31 31 22 22 13

**Answer**: (a)

**Explanation:**

This is a subtraction series with repetition. Each number repeats itself and then decreases by 9.

4 8 22 12 16 22 20 24

**Answer**: (c)

**Explanation:**

This is an alternating repetition series, with a random number, 22, interpolated as every third number into an otherwise simple addition series. In the addition series, 4 is added to each number to arrive at the next number.

9 12 11 14 13 16 15

**Answer**: (c)

**Explanation:**

This is a simple alternating addition and subtraction series. First, 3 is added, then 1 is subtracted, then 3 is added, 1 subtracted, and so on.

61 57 50 61 43 36 61

**Answer**: (e)

**Explanation:**

This is an alternating repetition series, in which a random number, 61, is interpolated as every third number into an otherwise simple subtraction series. Starting with the second number, 57, each number (except 61) is 7 less than the previous number.

20 20 17 17 14 14 11

**Answer**: (e)

**Explanation:**

This is a simple subtraction with repetition series. It begins with 20, which is repeated, then 3 is subtracted, resulting in 17, which is repeated, and so on.

84 78 72 66 60 54 48

**Answer**: (b)

**Explanation:**

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

3 8 13 18 23 28 33

**Answer**: (c)

**Explanation:**

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

11 16 21 26 31 36 41

**Answer**: (d)

**Explanation:**

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

75 65 85 55 45 85 35

**Answer**: (b)

**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.

21 25 18 29 33 18

**Answer**: (d)

**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.

6 20 8 14 10 8 12

**Answer**: (b)

**Explanation:**

This is an alternating addition and subtraction series. In the first pattern, 2 is added to each number to arrive at the next; in the alternate pattern, 6 is subtracted from each number to arrive at the next.

17 17 34 20 20 31 23

**Answer**: (e)

**Explanation:**

This is an alternating subtraction series with repetition. There are two different patterns here. In the first, a number repeats itself; then 3 is added to that number to arrive at the next number, which also repeats. This gives the series 17, 17, 20, 20, 23, and so on. Every third number follows a second pattern, in which 3 is subtracted from each number to arrive at the next: 34, 31, 28.

2 3 4 5 6 4 8

**Answer**: (d)

**Explanation:**

This is an alternating addition series with a random number, 4, interpolated as every third number. In the main series, 1 is added, then 2 is added, then 1, then 2, and so on.

9 11 33 13 15 33 17

**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.

2 8 14 20 26 32 38

**Answer**: (b)

**Explanation:**

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

9 16 23 30 37 44 51

**Answer**: (d)

**Explanation:**

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

8 11 21 15 18 21 22

**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.

28 25 5 21 18 5 14

**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.

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