Four times a number is 21 more than the number. What is the number?

Question

define a variable and write an equation to find each number then solve

Answer 1

If we let y represent the missing number, then we can represent "four times the number" as 4y and "21 more than the number" as 21 + y

Since these two quantities are equal to each other, we can write:

4y = 21 + y

To solve for y, we can subtract y from both sides of the equation:

4y - y = 21 + y - y

The result would be 3y = 21

Then we would divide both sides of the equation by 3:

3y/3 = 21/3

The final solution is:

y=7

To check: 4 * 7 is indeed equal to 7 + 21