Question
The average of 13 numbers is 108. The average of the
first 6 numbers is 77 and the average of the last 6 numbers is 42. What is the 7th number?Solution
Total sum of 13 numbers = 13 × 108 = 1404 Sum of first 6 numbers = 6 × 77 = 462 Sum of last 6 numbers = 6 × 42 = 252 According to question, => 1404 – (462 + 252) = 690
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