The mean of five numbers is 18. When a sixth number is added, the mean of all six numbers becomes 20. What is the sixth number?
Answer and explanation
Correct answer: D. 30
- Step 1: Total of the first five: 5 × 18 = 90. Step 2. Total of all six: 6 × 20 = 120. Step 3. The sixth number is 120 - 90 = 30. Answer: 30. Why not the others: 12: This is how far the sixth number is above the old mean of 18 once shared out, not the number itself: 2 × 6. 20: This is the new mean, not the new number. 38: This adds the old mean and the new mean.
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