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      Question

      Average of first 3 numbers is half the average of next 6

      numbers. If the average of all 9 numbers is 15, find the sum of the last 6 numbers.
      A 108 Correct Answer Incorrect Answer
      B 72 Correct Answer Incorrect Answer
      C 81 Correct Answer Incorrect Answer
      D 90 Correct Answer Incorrect Answer
      E 96 Correct Answer Incorrect Answer

      Solution

      Let the sum of the last 6 numbers be 'n'.
      (sum of first 3 numbers) Γ· 3 = 0.5 Γ— (n/6)
      β‡’ Sum of first 3 numbers = 0.25n
      Total sum = n + 0.25n = 1.25n
      Average of 9 numbers = 1.25n Γ· 9 = 15
      β‡’ 1.25n = 135
      β‡’ n = 108

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