Question
The average of 6 numbers is 25. The average of the first
four numbers is 20 and the average of the last three numbers is 30. Find the fourth number.Solution
Total of 6 numbers = 6 × 25 = 150 Sum of first 4 numbers = 4 × 20 = 80 Sum of last 3 numbers = 3 × 30 = 90 The 4th number is counted in both these sums. So: 80 + 90 − (4th number) = 150 170 − x = 150 x = 20 Answer: 4th number = 20.
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