Question

Find the average of 12 numbers if the average of the first 8 numbers is 21 and
the average of the last four numbers is 18.
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Answer 1

Step-by-step explanation:

Average of first 8 number = 21

Average of last 4 number = 18

If average of all 12 numbers is 18, then we have 8 x 3 = 24 extra from first eight numbers.

This extra is distributed over all 12 numbers increasing their average by 24/12 = 2.

=> Final average = 18 + 2 = 20