Question

Determine that Number
What is that number? If you multiply, it will be half & if you divide, then it will be double

Answer 1

1/2 is the number.

Let us assume, x is a number.
If you multiply number x by half then you will get x * 1/2 = x/2
and when you divide the number x by half (x / 1/2) = 2x.
So the number is 1/2.