When x is subtracted from each of 21, 22, 60 and 64, the numbers so obtained, in this order, are in proportion. What is the mean proportional between (x + 1) and (7x + 8)?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is Option 2 i.e. 24
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Concept |
Understanding |
Application |
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Mean proportion of a & b = √ab |
Suppose ‘x’ is subtracted from each of 21, 22, 60 and 64. |
Then, (21 – x)/(22 – x) = (60 – x)/(64 – x) ⇒ 21 × 64 – 85x + x2 = 22 × 60 – 82x + x2 ⇒ 3x = 21 × 64 – 22 × 60 ⇒ x = 7 × 64 – 22 × 20 ⇒ x = 8 Hence, mean proportion of (x + 1) i.e. 9 and (7x + 8) i.e. 64 = √(9 × 64) = 24 |