If a:b = 3:5 and a = 9, what is b?

If a:b = 3:5 and a = 9, what is b?

• A. 12
• B. 6
• C. 15
• D. 9

Answer: (C)

When two quantities are in a fixed ratio, each part scales together. Here, a corresponds to 3 parts and b to 5 parts. If a is 9, that means each part is 9 ÷ 3 = 3. Multiply by 5 parts for b: b = 5 × 3 = 15. So the value of b is 15.

When two quantities are in a fixed ratio, each part scales together. Here, a corresponds to 3 parts and b to 5 parts. If a is 9, that means each part is 9 ÷ 3 = 3. Multiply by 5 parts for b: b = 5 × 3 = 15. So the value of b is 15.