Second-Degree Equations

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jtwhite14: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Wed Jun 02, 2010 7:38 am

by jtwhite14 » Sun Jul 18, 2010 9:34 am

If (1/x) - (1/x+1) = (1/x+4), then x could be?

A. 0
B. -1
C. -2
D. -3
E. -4

OA C

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Source: Beat The GMAT — Problem Solving | Sun Jul 18, 2010 9:34 am

aloneontheedge: Senior | Next Rank: 100 Posts; Posts: 97; Joined: Thu Jan 28, 2010 2:07 am; Thanked: 9 times

by aloneontheedge » Sun Jul 18, 2010 9:38 am

jtwhite14 wrote:If (1/x) - (1/x+1) = (1/x+4), then x could be?

A. 0
B. -1
C. -2
D. -3
E. -4

OA C

Its straight forward.

after cross multiplying x+4 = x^2 + x
x = + or - 2
choose C

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sk818020: Master | Next Rank: 500 Posts; Posts: 214; Joined: Mon Mar 29, 2010 1:46 pm; Location: Houston, TX; Thanked: 37 times; GMAT Score:700

by sk818020 » Sun Jul 18, 2010 9:53 am

Another easy way to eliminate a bunch of the answers would be to think logically about the problem.

You cannot make any of the divisors in the equation zero because then the equation become undefined. So x cannot be 0, -1, or -4. So the answer cannot be A, B, or D. Then you can simply plug in the other two to get the correct answer.

Hope this helps.

Thanks,

Jared

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