A question related to the American TV series Trap is urgent ~ ~

This is a math game that the hero came up with, in the first episode of the second part. The male host gives the female host a letter, then calls the female host to ask her to think of a number, then multiplies this number by 2, adds 10, divides it by 2, and finally subtracts the number she thought before, which is 5, which is the number written in the letter. In fact, no matter what you think, the final result is 5.