If x is subtracted from each of 23, 39, 32 and 56, the numbers so obtained, in this order, are in proportion. What is the mean proportional between (x + 4) and (3x + 1)?
Show answer & explanation
Correct answer: C
Explanation
Correct Answer is option 3 i.e. 12.
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Concept |
Understanding |
Application |
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Mean proportion of a & b = √ab |
Suppose ‘x’ is subtracted from each of 23, 39, 32 and 56. |
Then, (23 – x)/(39 – x) = (32 – x)(56 – x) ⇒ 23 × 56 – 79x + x2 = 39 × 32 – 71x + x2 ⇒ 8x = 23 × 56 – 39 × 32 ⇒ x = 23 × 7 – 39 × 4 ⇒ x = 161 – 156 ⇒ x = 5 Hence, mean proportion of (4 + x) i.e. 9 and (3x + 1) i.e. 16 = √(9 × 16) = 12 |