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playground

by grandh01 » Thu Aug 30, 2012 2:32 pm
A square playground has the same
area as a rectangular playground that
is 30 meters longer but 20 meters
narrower. What is the length, in
meters, of a side of the square
playground?
(A) 10 square root 5
(B) 10 square root 6
(C) 25
(D) 50
(E) 60

OA is E[spoiler][/spoiler]
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by Jim@StratusPrep » Thu Aug 30, 2012 2:52 pm
x^2 = (x +30)(x-20)

x^2 = x^2 - 10x - 600

when you solve this you will get -60 -> the magnitude of this answer matches and honestly the sign does not matter for this question. Really the wording should be flipped though.
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by truplayer256 » Thu Aug 30, 2012 8:21 pm
Let each side of the square be x.

Area of square = x^2

Area of rectangular playground = (x + 30)(x - 20)

Equating the two:

x^2 = (x + 30)(x - 20)

x^2 = x^2 + 10x - 600

600 = 10x => x = 60 m

Choose E. Jim just made a slight mistake when he wrote -10x instead of +10x, so the answer should indeed be +60 m instead of -60 m.
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by mohan514 » Fri Aug 31, 2012 9:37 am
lenght can never be negative
so if at all we reach to such an answer we should consider absolute value
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