PCC Level 1 Practice Test

What is the sum of 4, 8, 12, 16, and 20, and what is the mean?

Sum = 60; mean = 12 Sum = 66; mean = 13.2 Sum = 60; mean = 15 Sum = 54; mean = 10.8

Correct Answer:

Sum = 60; mean = 12

Explanation:

Finding the sum and the mean of a small set of numbers, especially when they form an arithmetic sequence, is the goal here. The numbers 4, 8, 12, 16, and 20 increase by a constant amount, so there are five terms. To get the sum, use the fact that the average of the first and last terms times the number of terms gives the total: 5 × (4 + 20) / 2 = 5 × 12 = 60. You can also add them directly: 4 + 8 + 12 + 16 + 20 = 60. The mean (average) is the sum divided by the number of terms: 60 / 5 = 12. For an arithmetic sequence, the mean also equals the average of the first and last terms: (4 + 20) / 2 = 12. So the sum is 60 and the mean is 12.

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