If (x - y)^2 = 10, and if x^2 - y^2=2, then what is the value of (5x+5y)/(6x-6y) ?
Answer Choices:
A. 1/6
B. 1/5
C. 1/4
D. 1/3
E. 1/2
My approach is somehow wrong i guess because I don't get the right answer. I started with calculating x-y= +5, -5 (is this wrong?) and then plugging the value in the other equation! I feel so dumb right now because I can't see where I am wrong! Please explain!
Simplifying algebric expression
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- ilovemgmat
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(x^2-y^2)/(x-y)(x-y) = 2/10ilovemgmat wrote:If (x - y)^2 = 10, and if x^2 - y^2=2, then what is the value of (5x+5y)/(6x-6y) ?
Answer Choices:
A. 1/6
B. 1/5
C. 1/4
D. 1/3
E. 1/2
My approach is somehow wrong i guess because I don't get the right answer. I started with calculating x-y= +5, -5 (is this wrong?) and then plugging the value in the other equation! I feel so dumb right now because I can't see where I am wrong! Please explain!
=> (x-y)(x+y)/(x-y)(x-y) = 1/5
=> (x+y)/(x-y) = 1/5
hence, (5x+5y)/(6x+6y) = 5(x+y)/6(x-y)
= (5/6)(1/5)
= 1/6
- GmatMathPro
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Yes, that is wrong. It looks like you're trying to solve it by taking the square root of both sides, but 5 is not the square root of 10.
In any case, that is not the best way to solve it. Start by everything you can out of the expression (5x+5y)/(6x-6y). Then factor both equations and see if you can combine them in a way that gives you the value of your target expression.
In any case, that is not the best way to solve it. Start by everything you can out of the expression (5x+5y)/(6x-6y). Then factor both equations and see if you can combine them in a way that gives you the value of your target expression.
- GmatMathPro
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- ilovemgmat
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Yeah the square root of 10 is not 5. I feel like the dumbest person alive! Thanks!
GmatMathPro wrote:Yes, that is wrong. It looks like you're trying to solve it by taking the square root of both sides, but 5 is not the square root of 10.
In any case, that is not the best way to solve it. Start by everything you can out of the expression (5x+5y)/(6x-6y). Then factor both equations and see if you can combine them in a way that gives you the value of your target expression.
"Whoever one is, and wherever one is, one is always in the wrong if one is rude." ~Maurice Baring
Rudeness and sarcasm won't be entertained!
Rudeness and sarcasm won't be entertained!
We can easily solve by taking common
We have (x-y)2 = 10, x2-y2=2
Equation is (5x+5y)/(6x-6y), Taking 5 and 6 common in numerator and denominator we have
5/6 * (x+y)/(x-y) , Now multiply both numerator and denominator using x-y
5/6 * (x+y)(x-y)/(x-y)(x-y) = 5/6 * x2-y2/(x-y)2 = 5/6 * 2/10 = 1/6
Lot of practice problems has this equation used most of the time (x+y)(x-y) = x2-y2
Cheers,
SVD
We have (x-y)2 = 10, x2-y2=2
Equation is (5x+5y)/(6x-6y), Taking 5 and 6 common in numerator and denominator we have
5/6 * (x+y)/(x-y) , Now multiply both numerator and denominator using x-y
5/6 * (x+y)(x-y)/(x-y)(x-y) = 5/6 * x2-y2/(x-y)2 = 5/6 * 2/10 = 1/6
Lot of practice problems has this equation used most of the time (x+y)(x-y) = x2-y2
Cheers,
SVD