### A good answer might be:

0.31

# Base Two Positional Notation

Positional notation can also be used with a base other than ten. Here is a number written using base two:

    1 0 0  .  1 0 1

    1×22+ 0×21+ 0×20+  . 1×2-1+ 0×2-2+ 1×2-3

When a particular power of the base is not needed, the digit '0' is used for that position. If the base is two, the point '.' is called a binary point.

### QUESTION 4:

`What is 1×2-1 ?` (Express the answer in base ten notation).