Three less than twice a number is 21. Find that number

Answer 1

Let's call this mystery number X, and break down the sentence into parts.

twice a number: 2X

three less than twice a number: 2x - 3

three less than twice a number is 21: 2x-3 = 21

Now we solve for x.

2x-3 = 21

2x = 24

x = 12