CTS Placement Papers has a quantitative section. Questions on finding missing numbers in a sequence can be expected on these. Here is a list of sample questions with solution.

1) Find the missing number

3,8,_,38

If n is a given number in the series, the next number is 2n + 2
Hence third number is 2 * 8 + 2 = 18

2) Find the missing number

2,5,10,17,_

n th number in the aboe sequence is nsqure + 1
Hence 5th number is 5 square + 1 = 26

3) Find the missing number

4,7,13,21,_

Here 7 = 4 + 3
    13 = 7 + 6
    21 = 13 + 9

Hence next number = 21 + 12 = 33

4) Find the missing number

3,5,9,17,_

Here 5 = 3 + 2
     9 = 5 + 2 power 2
    17 = 9 + 2 power 3

Hence next number = 17 + 2 power 4 = 33

5) Find the missing number

2,6,10,18,_

Here if a = 2, then the series is

a, a + apower 2 , a + a power 3, a + a power 4

Then the next number is a + a power 5

= 34