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## GMAT prep simple ques

This topic has 2 expert replies and 1 member reply
jkelk Just gettin' started!
Joined
12 Mar 2012
Posted:
24 messages
GMAT prep simple ques Wed Mar 14, 2012 10:51 am
Elapsed Time: 00:00
• Lap #[LAPCOUNT] ([LAPTIME])
Hi

Thanks,
J
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### GMAT/MBA Expert

Anurag@Gurome GMAT Instructor
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Wed Mar 14, 2012 8:57 pm
jkelk wrote:
Hi

Thanks,
J
Apply the formula, (a + b)² = a² + b² + 2ab

[√(9 + √80) + √(9 - √80)]² = [√(9 + √80)]² + [√(9 - √80)]² + 2√(9 + √80)√(9 - √80)
= 9 + √80 + 9 - √80 + 2(81 - 80)
= 18 + 2
= 20

The correct answer is E.

_________________
Anurag Mairal, Ph.D., MBA
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jkelk Just gettin' started!
Joined
12 Mar 2012
Posted:
24 messages
Thu Mar 15, 2012 8:55 am
Hi Anurag,

Thanks for replying, could you please explain how you simplified 2√(9 + √80)√(9 - √80)
I seem to be missing this part.

Thanks,
J

### GMAT/MBA Expert

Anurag@Gurome GMAT Instructor
Joined
02 Apr 2010
Posted:
3835 messages
Followed by:
466 members
Thanked:
1749 times
GMAT Score:
770
Thu Mar 15, 2012 9:10 pm
jkelk wrote:
Hi Anurag,

Thanks for replying, could you please explain how you simplified 2√(9 + √80)√(9 - √80)
I seem to be missing this part.

Thanks,
J
Apply the formula, (a + b)(a - b) = a² - b²
2√(9 + √80)√(9 - √80) = 2√{(9 + √80)(9 - √80)}
= 2√{9² - (√80)²}
= 2√(81 - 80)
= 2√1
= 2

I hope it helps.

_________________
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

GMAT with Gurome
Career Advising with Gurome

Thanked by: jkelk

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