A number multiplied by 9 and decreased by 12 is equal to 72. Find the number.

Correct answer: 84/9. 9x − 12 = 72, so 9x = 84 and x = 84/9.

Background: Write the statement as an equation.

• 8: x = 8 gives 9(8) − 12 = 60, not 72.
• 9: x = 9 gives 9(9) − 12 = 69, not 72.
• 10: x = 10 gives 9(10) − 12 = 78, not 72.

Did you know? 84/9 = 28/3, about 9.33.

Memory trick: Add 12 first, then divide by 9.