What all set of number contain 0.5?

Answer 1

Any set that contains it!

It belongs to {0.5},

or {45, sqrt(2), 0.5, pi, -3/7},

or multiples of 0.5,

or square roots of 0.25,

or counting numbers divided by 2,

or rational numbers,

or real numbers,

or complex numbers,

etc.