Alex thinks of a number. he adds 18 then divides it by 2. he gets the same answer that he would have if he had multiplied the original number by 5. calculate the mystery number.

Alex thinks of a number

x

he adds 18 then divides it by 2

+ 18 : 2

he gets the same answer

=

if he had multiplied the original number by 5

x * 5

Put them all together

x + 18 : 2 = x * 5

x + 18/2 = 5x

x + 9 = 5x

9 = 5x - x

9 = 4x

9/4 = x