Question 1

15, 31, 63, 127, 255, (....)

Accepted Answer

Each number is double the preceding one plus 1. So, the next number is (255 x 2) + 1 = 511.

Question 2

1, 8, 27, 64, 125, 216, (....)

Accepted Answer

Numbers are 13, 23, 33, 43, 53, 63. So, the missing number is 73 = 343.

Question 3

3, 7, 6, 5, 9, 3, 12, 1, 15, (....)

Accepted Answer

There are two series, beginning respectively with 3 and 7. In one 3 is added and in another 2 is subtracted. The next number is 1 - 2 = -1.

Question 4

7, 8, 18, 57, 228, 1165, 6996

Accepted Answer

Let the given numbers be A, B, C, D, E, F, G. Then, A, A x 1 + 1, B x 2 + 2, C x 3 + 3, D x 4 + 4, E x 5 + 5, F x 6 + 6 are the required numbers. Clearly, 228 is wrong.

Question 5

1, 1, 2, 6, 24, 96, 720

Accepted Answer

Go on multiplying with 1, 2, 3, 4, 5, 6 to get next number. So, 96 is wrong.

Question 6

196, 169, 144, 121, 100, 80, 64

Accepted Answer

Numbers must be (14)2, (13)2, (12)2, (11)2, (10)2, (9)2, (8)2. So, 80 is wrong.

Question 7

445, 221, 109, 46, 25, 11, 4

Accepted Answer

Go on subtracting 3 and dividing the result by 2 to obtain the next number. Clearly, 46 is wrong.

Question 8

190, 166, 145, 128, 112, 100, 91

Accepted Answer

Go on subtracting 24, 21, 18, 15, 12, 9 from the numbers to get the next number. 190 - 24 = 166
166 - 21 = 145
145 - 18 = 127 [Here, 128 is placed instead of 127]
127 - 15 = 112
112 - 12 = 100 ... and so on.
 Therefore, 128 is wrong.

Question 9

19, 26, 33, 46, 59, 74, 91

Accepted Answer

Go on adding 7, 9, 11, 13, 15, 17 respectively to obtain the next number. So, 33 is wrong. It must be 35

Question 10

1, 3, 10, 21, 64, 129, 356, 777

Accepted Answer

A x 2 + 1, B x 3 + 1, C x 2 + 1, D x 3 + 1 and so on. So, 356 is wrong.

Question 11

6, 12, 48, 100, 384, 768, 3072

Accepted Answer

Each even term of the series is obtained by multiplying the previous term by 2. 2nd term = (1st term) x 2 = 6 x 2 = 12 4th term = (3rd term) x 2 = 48 x 2 = 96. 6th term = (5th term) x 2 = 384 x 2 =768. ∴ 4th term should be 96 instead of 100.

Question 12

40960, 10240, 2560, 640, 200, 40, 10

Accepted Answer

Go on dividing by 4 to get the next number. So, 200 is wrong.

Question 13

3, 7, 15, 39, 63, 127, 255, 511

Accepted Answer

Go on multiplying 2 and adding 1 to get the next number. So, 39 is wrong.

Question 14

64, 71, 80, 91, 104, 119, 135, 155

Accepted Answer

Go on adding 7, 9, 11, 13, 15, 17, 19 respectively to obtain the next number. So, 135 is wrong.

Question 15

15, 16, 34, 105, 424, 2124, 12756

Accepted Answer

2nd term = (1st term) x 1 + 1 = 15 x 1 + 1 = 16. 3rd term = (2nd term) x 2 + 2 = 16 x 2 + 2 = 34. 4th term = (3th term) x 3 + 3 = 34 x 3 + 3 = 105. 5th term = (4th term) x 4 + 4 = 105 x 4 + 4 = 424 6th term = (5th term) x 5 + 5 = 424 x 5 + 5 = 2125 ∴ 6th term should 2125 instead of 2124.

Question 16

10, 26, 74, 218, 654, 1946, 5834

Accepted Answer

2nd term = (1st term) x 3 - 4 = 10 x 3 - 4 = 26. 3rd term = (2nd term) x 3 - 4 = 26 x 3 - 4 = 74. 4th term = (3th term) x 3 - 4 = 74 x 3 - 4 = 218. 5th term = (4th term) x 3 - 4 = 218 x 3 - 4 = 650. ∴ 5th term must be 650 instead of 654.

Question 17

2880, 480, 92, 24, 8, 4, 4

Accepted Answer

Go on dividing by 6, 5, 4, 3, 2, 1 respectively to obtain the next number. Clearly, 92 is wrong.

Question 18

3, 7, 15, 27, 63, 127, 255

Accepted Answer

Go on multiplying the number by 2 and adding 1 to it to get the next number. So, 27 is wrong.

Question 19

835, 734, 642, 751, 853, 981, 532?

Accepted Answer

In each number except 751, the difference of third and first digit is the middle one .

Question 20

8, 27, 64, 100, 125, 216, 343?

Accepted Answer

The pattern is 23, 33, 43, 53, 63, 73. But 100 is not a perfect cube

Odd Man Out and Series Questions