Math CentralQuandaries & Queries


Question from jean, a student:

the average of 9 is 54.if 84 and 90 are added to the set of numbers , what will be the resulting average?

Hi Jean,

The average of 9 numbers is 54 so if you add the 9 numbers and then divide by 9 you get 54. Hence the sum of the 9 numbers must be 9 × 54 = 486.

Two more numbers, 84 and 90 are added to the list. What is the sum of all 11 numbers? What is their average?

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