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

A. 160

What is the missing number in the series: 2, 6, 12, 20, ?, 42

B. 32

Find the missing letter in the series: a, e, i, o, ?

A. U

Identify the missing letter in the series: Z, X, V, T, ?

A. R

Complete the series: B, D, F, H, ?

A. J