Find the missing number in the series: 5, 10, 20, 40, ?

A. 80

What number should replace the question mark in the series: 1, 1, 2, 3, 5, ?

A. 7

Identify the missing number in the series: 12, 24, 48, ?, 192.

A. 96

What is the missing number in the series: 100, 90, 80, 70, ?

A. 60

What is the next number in the series: 10, 20, 30, 40, ?

B. 50