what is the value!

BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

This topic has expert replies

Post new topic Post Reply

Previous Topic Next Topic

Ozlemg: Master | Next Rank: 500 Posts; Posts: 407; Joined: Tue Jan 25, 2011 9:19 am; Thanked: 25 times; Followed by:7 members

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!

Quote

Source: Beat The GMAT — Problem Solving | Mon Jul 04, 2011 1:06 pm

edvhou812: Master | Next Rank: 500 Posts; Posts: 143; Joined: Sat Nov 06, 2010 9:06 pm; Thanked: 10 times; Followed by:1 members

by edvhou812 » Mon Jul 04, 2011 4:18 pm

I got -1.68, or E. Just plug in 1.4 whenever you see 'X'.

Quote

gmatblood: Master | Next Rank: 500 Posts; Posts: 489; Joined: Tue Jul 05, 2011 11:10 am; Thanked: 28 times; Followed by:5 members

by gmatblood » Tue Jul 05, 2011 12:01 pm

a) -0.28

Quote

Jim@Knewton: GMAT Instructor; Posts: 23; Joined: Thu Jun 09, 2011 11:34 pm; Location: New York City; Thanked: 17 times; Followed by:6 members

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.

Best, Jim
Please "thank" this post if it helps you!
https://www.knewton.com/people/jims

Quote

mbacult: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sun Jun 26, 2011 5:05 am; Thanked: 1 times

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

Quote

Jim@Knewton: GMAT Instructor; Posts: 23; Joined: Thu Jun 09, 2011 11:34 pm; Location: New York City; Thanked: 17 times; Followed by:6 members

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

Best, Jim
Please "thank" this post if it helps you!
https://www.knewton.com/people/jims

Quote

artistocrat: Master | Next Rank: 500 Posts; Posts: 152; Joined: Wed Mar 12, 2008 4:36 pm; Thanked: 8 times; Followed by:2 members

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.