Question
Average of first 3 numbers is three times the average of
next 6 numbers. If the average of all nine numbers is 15, find the sum of the last 6 numbers.Solution
Let the sum of the last 6 numbers be 'n'.
(sum of first 3 numbers) ÷ 3 = 3 × (n/6)
⇒ Sum of first 3 numbers = 1.5n
Total sum = n + 1.5n = 2.5n
Average of 9 numbers = 2.5n ÷ 9 = 15
⇒ 2.5n = 135
⇒ n = 54
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