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help!!!

by jayanti » Fri Aug 12, 2011 7:52 am
The operation * is defined by the equation x*y = (x-y)/(x+y), where y ≠ -x. If 3*y = 5*4,then y =
A. 1/9
B. 4/15
C. 5/12
D. 12/5
E. 15/4

I cant figure this one out.......
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by Anurag@Gurome » Fri Aug 12, 2011 9:06 am
jayanti wrote:The operation * is defined by the equation x*y = (x-y)/(x+y), where y ≠ -x. If 3*y = 5*4,then y =
Given that, x*y = (x-y)/(x+y)

Thus, 3*y = (3 - y)/(3 + y)
And, 5*4 = (5 - 4)/(5 + 4) = 1/9

So, (3 - y)/(3 + y) = 1/9
--> 9(3 - y) = (3 + y)
--> (27 - 9y) = (3 + y)
--> 10y = 24
--> y = 24/10 = 12/5

The correct answer is D.
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by jayanti » Fri Aug 12, 2011 10:03 am
Hi Sir, Could you pls explain the

3*y = (3 - y)/(3 + y)
And, 5*4 = (5 - 4)/(5 + 4) = 1/9

I dont seem to get it:(

Thanks a lot...
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by Anurag@Gurome » Fri Aug 12, 2011 10:15 am
jayanti wrote:Hi Sir, Could you pls explain the

3*y = (3 - y)/(3 + y)
And, 5*4 = (5 - 4)/(5 + 4) = 1/9

I don't seem to get it:(

Thanks a lot...
The question defines the operation x*y as (x - y)/(x + y).
Hence, a*b = (a - b)/(a + b)
Similarly, 5*4 = (5 - 4)/(5 + 4)
And, 3*y = (3 - y)/(3 + y)

To put it simply replace x with left operand and replace y with right operand in the expression.
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