The mean of five numbers is . Four of the numbers are . What is the fifth number?

Answer and explanation

Correct answer: D. 10

  1. Step 1: For a mean of , the five values must total .
  2. Step 2: Add the four known values: .
  3. Step 3: Find the fifth number by taking the difference: .
Answer
10.
Why not the others: - 15 adds rather than subtracts the constant term in the final step in . - 13 is the mean of the numbers. - 5 omits the factor of 2 in the denominator during simplification.

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