Series Problems

Series Problems

Dear Reader,
Below are four problems on series, you have to find the next number of given series.

Question 1

18, 35, 71, 141, 283, ?

a) 565 b) 493 c) 387 d) none of these

Answer : a) 565.

Solution :

Each number of the given series is twice the preceding one with 1 added or subtracted alternately.

1st number = 18
2nd number = 18 x 2 - 1 = 35
3rd number = 35 x 2 + 1 = 71
4th number = 71 x 2 - 1 = 141
5th number = 141 x 2 + 1 = 283
Required 6th number = 283 x 2 - 1 = 565.

Question 2

14, 18, 17, 16, 20, 14, 23, 12, 26, ?

a) 10 b) 29 c) 32 d) none of these

Answer : a) 10.

Solution :

There are two series beginning respectively with 14 and 18.

In one 3 is added and in another 2 is subtracted.

And the series are 14, 17, 20, 23, 26,.. and 18, 16, 14, 12,...

14 + 3 = 17, 17 + 3 = 20, 20 + 3 = 23, 23 + 3 = 26,..
18 - 2 = 16, 16 - 2 = 14, 14 - 2 = 12, 12 - 2 = 10,..

Hence, the required next number is 10.

Question 3

20, 10, 26, 20, 32, 40, 38, ?

a) 46 b) 50 c) 32 d) none of these

Answer : d) none of these

Solution :

There are two series (20, 26,32, 38,...) and (10, 20, 40,..)

One is increasing by 6 and another is multiplied by 2.

20 + 6 = 26, 26 + 6 = 32, 32 + 6 = 38
10 x 2 = 20, 20 x 2 = 40, 40 x 2 = 80.

So, the required next number is 80.

Question 4

16, 48, 24, 72, 36, 108, ?

a) 81 b) 54 c) 216 d) 126

Answer : b) 54

Solution :

Numbers in the given series are alternately multiplied by 3 and divided by 2.

i.e.,1st number = 16
2nd number = 16 x 3 = 48
3rd number = 48 / 2 = 24
4th number = 24 x 3 = 72
5th number = 72 / 2 = 36
6th number = 36 x 3 = 108
Required 7th number = 108 / 2 = 54.