When x is subtracted from each of 19, 28, 55 and 91, the numbers so obtained in this order, are in proportion. What is the mean proportion between (x + 9 ) and x2 ?
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Correct answer: C
Explanation
The correct answer is option 3 i.e. 28
According to the question,
(19 - x) : (28 - x) :: (55 - x) : (91 - x)
product of extremes = product of means.
(19 - x) × (91 - x) = (55 - x) × (28 - x)
1729 - 19x - 91x + x2 = 1540 - 55x - 28x + x2
-110x + 1729 = 1540 - 83x
27x = 189
x = 7
Mean proportion of a and b is .
= = 28.