Complete the proportion: 5 is to 25 as 8 is to what number?

Complete the proportion: 5 is to 25 as 8 is to what number?

• A. 8
• B. 5
• C. 10
• D. 40

Answer: (D)

This tests recognizing a constant multiplier in a proportion. The pair 5 to 25 has a ratio of 1 to 5, since 25 is five times as large as 5. To keep the same relationship with 8, multiply 8 by 5, giving 40. You can also see it by cross-multiplying: 5/25 equals 8/x, which reduces to 1/5 = 8/x, so x = 40. The missing number is 40.

This tests recognizing a constant multiplier in a proportion. The pair 5 to 25 has a ratio of 1 to 5, since 25 is five times as large as 5. To keep the same relationship with 8, multiply 8 by 5, giving 40. You can also see it by cross-multiplying: 5/25 equals 8/x, which reduces to 1/5 = 8/x, so x = 40. The missing number is 40.