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      Question

      The average of 18 numbers is 70. The first eight

      numbers have an average of 90, and the last five numbers have an average of 48. The eleventh number exceeds the tenth number by 20%, and the twelfth number is reduced by (50/9)% from the eleventh number. Determine the value of the eleventh number.
      A 84 Correct Answer Incorrect Answer
      B 96 Correct Answer Incorrect Answer
      C 108 Correct Answer Incorrect Answer
      D 120 Correct Answer Incorrect Answer
      E 132 Correct Answer Incorrect Answer

      Solution

      Let tenth number is 10x
      So, eleventh number = 1.20 Γ— 10x = 12x
      Twelfth number = 850/9 Γ— 1/100 Γ— 12x = 34x/3
      So, 10x + 12x + 34x/3
      = 70 Γ— 18 – 8 Γ— 90 – 5 Γ— 48
      = 1260 – 720 – 240
      = 300
      Or, 100x/3 = 300
      Or, x = 9
      So, eleventh number = 12 Γ— 9 = 108

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