When x is subtracted from each of 55, 50, 23 and 22, the resulting numbers, in this order, are in proportion. What is the fourth proportion of 3, 7 and x?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 35 .
Let x satisfy (55 − x) : (50 − x) = (23 − x) : (22 − x)
(55 − x)(22 − x) = (50 − x)(23 − x)
1210 − 77x + x2 = 1150 − 73x + x2
1210 − 77x = 1150 − 73x
−77x + 73x = 1150 − 1210
−4x = −60
x = 15
Fourth proportional y of 3, 7 and x satisfies 3 : 7 = x : y
y = (7 × x) / 3 = (7 × 15) / 3 = 35