What is the next number in the series: 3, 7, 15, 31, ?

A. 63

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

C. 80

What number should replace the question mark in the series: 1, 4, 9, 16, ?, 36

A. 25

What is the missing number in the series: 10, 20, 40, 80, ?, 320

A. 160

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

B. 50