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    Question

    Average of 20 numbers is 90. Average of first 8 numbers

    is 81 while average of last nine numbers is 40. If ninth number is 25% less than the tenth number which is equal to the eleventh numbers then find the tenth number.
    A 278 Correct Answer Incorrect Answer
    B 298 Correct Answer Incorrect Answer
    C 288 Correct Answer Incorrect Answer
    D 208 Correct Answer Incorrect Answer

    Solution

    Sum of ninth, tenth and eleventh number = 20 × 90 – 8 × 81 – 9 × 40 = 792 Let tenth number = x = eleventh number So, ninth number = 0.75 × x = 0.75x So, x + 0.75x + x = 792 Or, 2.75x = 792 Or, x = 288

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