Question
The mean of 15 values is 72. The mean of the first seven values is 62, and the mean of the last five values is 86. The eighth value equals 25% of the ninth, and the tenth value is 75% more than the ninth. Determine the ninth value.
Solution
Let ninth number is x Eighth number = 0.25x Tenth number = 1.75x According to question; x + 0.25x + 1.75x = 15 × 72 – 7 × 62 – 5 × 86 = 216 Or, 3x = 216 Or, x = 72
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