The mean of five numbers is 18. When a sixth number is added, the mean becomes 20. What is the sixth number?
Answer and explanation
Correct answer: B.
- Step 1: Calculate the total sum of the first five numbers: .
- Step 2: Calculate the total sum of all six numbers: .
- Step 3: Subtract to find the value of the sixth number: .
Answer
.
Why not the others: incorrectly computes ; adds only the difference in means ; adds .
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