Number Series Solved Problems

Number Series 

1. Look at the series and find the exact number.
80, 10, 70, 15, 60,.... 

Answer : 20
Explanation :
This is an alternating addition and subtraction series.
In the first pattern, 10 is subtracted from each number to arrive at the next.
In the second, 5 is added to each number to arrive at the next.

2.  Look at the series and find the pair numbers.
75 65 85 55 45 85 35 ....... 

Answer : 25 85
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 arrived at the next.

3.  Which number would replace underline mark in the series?
3,9, 21, ___, 93.

Answer : 45
Explanation :
First difference is 6 and second is 12.
But if we take third as 18, then fourth difference will be 24.
Then 93 can not be the last term.
So we have to take the difference as 6, 12, 24 and 48.
So 21 + 24 = 45.

4.  Look at this series and find the pair numbers.
28 25 10 21 18 10 14 .......

Answer : 11 10
Explanation :
This is an alternating subtraction series with the interpolation of a random number 10, as every third number.
In the subtraction series, 3 is subtracted, then 4, then 3, and so on.

5.  Look at this series: 70 20 60 25 50 .........
What number should fill the blank?

Answer : 30
Explanation :
This is an alternating addition and subtraction series.
In the first pattern, 10 is subtracted from each number to arrive at the next.
In the second pattern, 5 is added to each number to arrive at the next.

6. Look at this series: 1.5, 2.3, 3.1, 3.9, ?
What number should come next?

Answer: 4.7
Explanation:
In this simple addition series, each number increases by 0.8.

7. 36, 34, 30, 28, 24, ?
What number should come next?

Answer: 22
Explanation:
Pattern in the series is, -2, -4, -2, -4. So next term will be -2.
Hence, 24 - 2 = 22.

8.  Find the missing letter in the given series:
8 : 81 :: 64 : ?

Answer: 625
Explanation:
The relationship is
xy : (x + 1)y + 1
Since 64 = 43
So, required number = (4 + 1)3 + 1
= 54 = 625.

9.  Look at this series and find the pair numbers.21 25 18 29 33 18......

Answer : 37
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.

10.  Look at this series and find exact number.
2, 6, 14, 26, ...., 62.

Ans: 42
Explanation :
This pattern is +4, +8, +12, +16,....
Therefore, missing number is 26 + 16 = 42.

11.  Look at this series and find the pair numbers.
21 25 30 29 33 30......

Answer : 37 41
Explanation :
This is a simple addition series with a random number 30, interpolated as every third number.
In the series, 4 is added to each number except 30, to arrive at the next number.

12.  Find the odd man out.
16, 25, 36, 72, 144, 196, 225.

Ans: 72
Explanation :
Each of the numbers except 72, is a perfect square.

13. Insert the missing number.
2, 6, 12, 20, 30, 42, 56,.....

Ans: 72
Explanation :
The pattern is 1 x 2, 2 x 3, 3 x 4, 4 x 5, 5 x 6, 6 x 7, 7 x 8.
So, the next number is 8 x 9 = 72.

14.  Fill the blank in the middle of the series.
6, 12, 21, ...... , 48. 

Ans: 33
Explanation :
The pattern is +6, +9, +12, +15.
The missing term is 21+12 = 33.

15.  Look at the series and find the exact number.
1 10 7 20 13 30 19 ? ? 

Answer : 40 25
Explanation :
In the first series (odd position value), 6 is added to each number to arrive at the next.
In the second series (even position value), 10 is added to each number to arrive at the next.