If 39 x 39 varies inversely as y2 1 and equal to 6 when 39 y 39 8 Find 39 x 39 when 39 y 39 7 ........

Quantitative Aptitude ( CCS) Number System

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If 'x' varies inversely as (y² + 1) and equal to 6 when 'y' = 8. Find 'x' when 'y' = 7?

7.8

11.3

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Explanation:

Given that x varies inversely as y² + 1.
In math form
x ∞ 1/y^2+1
x =k/y^2+1
k = x (y² + 1) .....(1)
Now plug y = 8 and x = 6 into above equation
k = 6 (8² + 1)
k = 6 (64 +1)
k = 6 (65)
k = 390
Now substitute k = 390 into equation (1)
390 = x (y² + 1) .....(2)
Now put y = 7 into the equation 2
390 = x (7² + 1)
390 = x (49 +1)
390 = x (50)
x =390/50
So, our answer is x = 7.8