Number in sequence 3,-6,12,4,20

Number in sequence 3,-6,12,4,20 is expanded in the following way

Step-by-step explanation:

There are 2 series clubbed together

Odd place series 3 12 20?

Even place series - 6 4?

These numbers are related in the following way, beginning with 3:

First, we subtract 9 to get - 6

3 - 9 = - 6

Next, we add 18

-6 + 18 = 12

To get from 12 to 4, we subtract 8:

12 - 8 = 4

and to get from 4 to the final number of 20, we must add 16

4 + 16 = 20

We need to examine the numbers that we add/take away in the sequence to find a pattern so we can predict the next number.

Even place numbers are getting subtracted starting from number 9 and it kept on decreasing for successive odd positions.

Odd place numbers are getting added with twice the number which has been previously subtracted ...

hence next number will be

20-7 = 13 ...