Look at this series: 4, 7, 25, 10, __ , 20, 16, 19.

Question

Which number should fill the blank?

13

15

20

28

Answer 1

In the first series, number increments by 3, and the number appears in the 1,2,4,5,7 positions. Series starts with 4. Numbers in this series are 4,7,10,13,16,19
In the second series, the number appears at a multiple of 3 positions. i.e. 3,6,9 ..and it decreases by 5. Starting with 25. So the numbers in this series are 25,20,15 etc.
Combining them together, series becomes 4,7,25,10,13,20,16,19
This kind of series is also known as skip number series and are at times confusing to solve but not very difficult.

Your answer is A.)13

Answer 2

Two series alternate here.

In the first series, 3 is added to each number to arrive at the next.

4, 7, 10 , __ , 16, 19

In the second series, 5 is subtracted from each number to arrive at the next.

25 , 20 ...

Your number is in the first series.

So you have to add 3 to 10

13