Series Completion

In this type of questions, one term in the number series is wrong. Find out the wrong term.

1,3,12,25,48

Answer: (c)

The terms of the series are (l2 - 02), (22 - l2), (42 - 22), (62 - 32) and (82 - 42).

So, 25 is wrong and must be replaced by (62 - 32) i.e. 27.

2, 5, 10, 50, 500, 5000

Answer: (d)

Each term of the series is the product of the preceding two terms.

So, 5000 is wrong and must be replaced by (50 x 500) i.e. 25000.

125, 126, 124, 127, 123, 129

Answer: (d)

The correct pattern is + 1, - 2, + 3, - 4, + 5.

So, 129 is wrong and must be replaced by (123 + 5) i.e. 128.

2, 5, 10, 17, 26, 37, 50, 64

Answer: (d)

The terms of the series are (12 + 1), (22 + 1), (32 + 1), (42 + 1), (52 + 1), (62 + 1),

(72+1),.....

So, 64 is wrong and must be replaced by (82 + 1) i.e. 65.

105, 85, 60, 30, 0, – 45, – 90

Answer: (c)

The correct pattern is - 20, - 25, - 30,.....

So, 0 is wrong and must be replaced by (30 - 35) i.e. - 5.

3, 4, 10, 32, 136, 685, 4116

Answer: (b)

The correct pattern is x 1 + 1, x 2 + 2, x 3 + 3, x 4 + 4,.....

So, 32 is wrong and must be replaced by (10 x 3 + 3) i.e. 33.

1, 2, 4, 8, 16, 32, 64, 96

Answer: (d)

Each term of the series is obtained by multiplying the preceding term by 2.

So, 96 is wrong and must be replaced by (64 x 2) i.e. 128.

8, 13, 21, 32, 47, 63, 83

Answer: (d)

The correct pattern is + 5, + 8, + 11, + 14,.....

So, 47 is wrong and must be replaced by (32 + 14) i.e. 46.

6, 15, 35, 77, 165, 221

Answer: (c)

The terms of the series are products of two consecutive prime numbers i.e. (2 x 3),

(3 x 5), (5 x 7), (7 x 11),.....

So, 165 is wrong and must be replaced by (11 x 13) i.e. 143.

121, 143, 165, 186, 209

Answer: (c)

Each term in the series is obtained by adding 22 to the preceding term.

So, 186 is wrong and must be replaced by (165 + 22) i.e. 187.