CEMC Cayley

Algebra Difficulty 2.1 Junior Find the answer

Ten numbers have an average (mean) of 87. Two of those numbers are 51 and 99. What is the average of the other eight numbers?

Your answer

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Solution

Since 10 numbers have an average of 87, their sum is $10 \times 87 = 870$ . When the numbers 51 and 99 are removed, the sum of the remaining 8 numbers is $870 - 51 - 99$ or 720. The average of these 8 numbers is $\frac{720}{8} = 90$ .

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