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what is the value!

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what is the value!

by Ozlemg » Mon Jul 04, 2011 1:06 pm
What is the value of 0.5(x^2) - 1.4x - 0.7 for x = 1.4 ?
(A) -0.28
(B) -0.54
(C) -0.72
(D) -1.42
(E) -1.68
The more you suffer before the test, the less you will do so in the test! :)
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by edvhou812 » Mon Jul 04, 2011 4:18 pm
I got -1.68, or E. Just plug in 1.4 whenever you see 'X'.
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by gmatblood » Tue Jul 05, 2011 12:01 pm
a) -0.28
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by Jim@Knewton » Tue Jul 05, 2011 2:11 pm
0.5(x^2) - 1.4x - 0.7 for x = 1.4
=> 0.5*(1.4^2) - (1.4^2) - 0.7
=> -0.5*(1.4^2)- 0.7 ..........but -0.5*(1.4^2) = - (1.4)*0.7
=> -0.7*(1.4+1)
[spoiler]=> -1.68
Hence E[/spoiler]
In such questions, usually look for a way to solve rather than compute - computations can be time consuming and comparatively more prone to error! :-)
Last edited by Jim@Knewton on Tue Jul 05, 2011 4:51 pm, edited 1 time in total.
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by mbacult » Tue Jul 05, 2011 4:29 pm
From earlier post-
>>=> -0.5*(1.4^2)- 0.7 ..........but -0.5*(1.4^2) = - (1.4)*0.7
>>=> -0.7*(1.4-1)

Instead of the last line above, it should be => -0.7*(1.4+1)
giving the ans -1.68
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by Jim@Knewton » Tue Jul 05, 2011 4:59 pm
Thank you mbacult - just edited the typo!

...and gmatblood, I thought you posted the OA -that would be the case if:
0.5(x^2) - 1.4x + 0.7 for x = 1.4
=> 0.5*(1.4^2) - (1.4^2) + 0.7
=> -0.5*(1.4^2)+ 0.7 ..........but -0.5*(1.4^2) = - (1.4)*0.7
=> -0.7*(1.4-1)
=> -0.28
for the +0.7
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by artistocrat » Tue Jul 05, 2011 6:04 pm
-1.68. Factor or don't factor, it's about the same amount of time. Knowing squares helps. eg.14x14. Seeing that 0.7 is a factor of 1.4 helps. But like I said this could just be calculated. Unlikely to see something this easy on the GMAT.
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by worldpeace93 » Tue Jul 05, 2011 10:23 pm
I got answer as -1.68
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