If x is added to each of 12, 28, 21 and 45, the numbers so obtained, in this order, are in proportion. What is the mean proportional between (x + 3) and (4x + 1)?
Show answer & explanation
Correct answer: A
Explanation
Correct Answer is option 1 i.e. 15
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Concept |
Understanding |
Application |
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Mean proportion of a & b = √ab |
‘x’ is added to each of 12, 28, 21 and 45. |
Then, (12 + x)/(28 + x) = (21 + x)/(45 + x) ⇒ 45 × 12 + 57x + x2 = 21 × 28 + 49x + x2 ⇒ 8x = 21 × 28 – 45 × 12 ⇒ 8x = 48 ⇒ x = 6 Hence, mean proportion of (x + 3) i.e. 9 and (4x + 1) i.e. 25 = √(9 × 25) = 15 |