If 4x/5 = 3y/8, find x : y.

Correct answer: 15:32. Cross-multiplying gives 4x × 8 = 3y × 5, so 32x = 15y and x : y = 15 : 32.

Background: If a/b = c/d, then a × d = b × c.

• 32:15: 32:15 is the reverse of the correct ratio.
• 16:15: 16:15 does not satisfy the equation.
• 5:8: 5:8 does not satisfy the equation.

Did you know? For a ratio x : y, keep x on one side and y on the other.

Memory trick: 32x = 15y → x : y = 15 : 32.