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The average of 9 numbers is 16. When a tenth number is added, the average rises to 17. What is the value of the tenth number?

1. 26
2. 9
3. 16
4. 30

Correct answer: 26

Solution

The sum of the first nine numbers is 9 x 16 = 144 and the sum of all ten is 10 x 17 = 170. The tenth number is the difference, 170 - 144 = 26.

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