Question

50% of a certain number is 23. What is the number?

Answer 1

50% = 50/100 = 1/2 (one half)

One half of a certain number is 23.
Note that the opposite of halving is doubling. (if you do both they cancel out)
Let's double 23 to get 46.
Half of 46 is 23.
Our number is 46.

Answer 2

Take that certain number as 'a'

50% = 0.5

0.5a = 23

Divde both sides by 0.5

0.5a = 23
/0.5    /0.5

a = 46