Question
Average of 15 numbers is 78. The average of the first
seven is 74 and of the last five is 92. The eighth number is 40% of the ninth, and the tenth number is 60% more than the ninth. Find the ninth number.Solution
Let ninth number is x Eighth number = 0.40x Tenth number = 1.60x According to question; x + 0.40x + 1.60x = 15 × 78 – 7 × 74 – 5 × 92 = 192 Or, 3x = 192 Or, x = 64
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