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# simplify

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Director
Joined: 25 Oct 2008
Posts: 592

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Location: Kolkata,India

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09 Jun 2009, 19:33
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If x = 4 and y = 16, then sq. root of (x+y/xy) is closest to which of the following ?

(A) 1/3
(B) 1/2
(C) 3/4
(D)7/8
(E) 1

[spoiler]OA:B[/spoiler]

Ok so i got stuck in the last step.Simplified and got sq root of 5/4.Now what if I have no clue of wat the value of sq root of 5 is?My ans was C because i know sq root of 4 is 2.So sq root of 5 should be a value 2+.I already have the denominator as 4.So C.CLearly the logic is wrong.
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http://gmatclub.com/forum/countdown-beginshas-ended-85483-40.html#p649902

Kudos [?]: 1232 [0], given: 100

Current Student
Joined: 03 Aug 2006
Posts: 115

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09 Jun 2009, 22:03
I think you were on the right track. For me I have memorized the sqrt of 2,3 and 5. The sqrt of 5 is 2.25. Hence answer is

$$\frac{2.25}{4} = \frac{9}{16}$$

which is closer to 1/2

Kudos [?]: 320 [0], given: 3

Manager
Joined: 28 Jan 2004
Posts: 201

Kudos [?]: 30 [0], given: 4

Location: India

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09 Jun 2009, 22:42
Just another way to look at it is....

by substituting X and Y we get .. Sqrt(5/16). Instead of performing square root of this , i will square the answer choices as squaring is easy.

1/3 give 1/9
1/2 gives 1/4
3/4 gives 9/16
7/8 gives 49/64
1 gives 1.

9/16 is closed to 5/16. So this should be answer. I am sure out of 5 atleast 3 will be definetly no-no for remianign 2 (if requird)you can perform a actual divide. This takes less time.

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Director
Joined: 25 Oct 2008
Posts: 592

Kudos [?]: 1232 [0], given: 100

Location: Kolkata,India

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21 Jun 2009, 02:59
mdfrahim:i liked your approach but the OA is (b) not (c).NOW how do you explain?
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http://gmatclub.com/forum/countdown-beginshas-ended-85483-40.html#p649902

Kudos [?]: 1232 [0], given: 100

Senior Manager
Joined: 08 Jan 2009
Posts: 324

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21 Jun 2009, 08:25
Agree with B

by substituting X and Y we get .. Sqrt(5/16) or 1/4 by Sqrt(5)

1/4 Sqrt(4) = 1/2 and 1/4 Sqrt(9) = 3/4 .

So our answer lie b/w this.

Scanning through the choice u will see A,D, E are out since outside our range.

Then among B and C . Definetly ours is closer to B.

Kudos [?]: 191 [0], given: 5

Intern
Joined: 04 Mar 2008
Posts: 42

Kudos [?]: 3 [0], given: 6

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22 Jun 2009, 15:56
tejal777 wrote:
If x = 4 and y = 16, then sq. root of (x+y/xy) is closest to which of the following ?

(A) 1/3
(B) 1/2
(C) 3/4
(D)7/8
(E) 1

[spoiler]OA:B[/spoiler]

Ok so i got stuck in the last step.Simplified and got sq root of 5/4.Now what if I have no clue of wat the value of sq root of 5 is?My ans was C because i know sq root of 4 is 2.So sq root of 5 should be a value 2+.I already have the denominator as 4.So C.CLearly the logic is wrong.

looks like you just missed the last step of the calculation.

Kudos [?]: 3 [0], given: 6

Re: simplify   [#permalink] 22 Jun 2009, 15:56
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