Q.$\text{Look at this series: } 2,\ 1,\ \left(\frac{1}{2}\right),\ \left(\frac{1}{4}\right),\ \ldots \text{ What number should come next?}$

This is a simple division series; each number is one-half of the previous number.

In other terms to say, the number is divided by 2 successively to get the next result.

4/2 = 2 2/2 = 1 1/2 = 1/2 (1/2)/2 = 1/4 (1/4)/2 = 1/8 and so on.