1 , _ , 5 , 10 , 20 , 40 , 80

Question

find the missing numbers

Answer 1

The series is 1 , _ , 5, 10 , 20 , 40 , 80

The pattern of the series is to find next number is sum of all previous numbers.

Let missing number = x

Missing number is x  + 1 = 5

x  = 5 - 1

x  = 4

Check

First number 1 + 4 = 5

Second number 1 + 4 + 5 = 10

Third number 1 + 4 + 5 + 10 = 20

Fourth number 1 + 4 + 5 + 10 + 20 = 40

Fifth number 1 + 4 + 5 + 10 + 20 + 40  = 80

Missing term is 4.