What is the missing number in the series 4, 8, ?, 32, 64?

Explanation

1. 01

   Test the ratio: $8 \div 4 = 2$ and $64 \div 32 = 2$.

2. 02

   So each term doubles: the missing term is $8 \times 2 = 16$, and $16 \times 2 = 32$ checks.