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Root(80)+root(125)

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Root(80)+root(125) [#permalink] New post 01 Oct 2012, 04:02
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00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

91% (01:38) correct 9% (01:12) wrong based on 353 sessions
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Re: Root(80)+root(125) [#permalink] New post 01 Oct 2012, 06:43
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Whe we deal with this problems may be the best thing to do is to break the number into factors

\sqrt{80}=\sqrt{2*5*2*2*2} ---> \sqrt{4*4*5} ---> 4\sqrt{5}

\sqrt{125} = \sqrt{25 *5} -----> 5 \sqrt{5}

4\sqrt{5} + 5 \sqrt{5} = 9\sqrt{5}

A should be the answer
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Re: Root(80)+root(125) [#permalink] New post 03 Oct 2012, 23:50
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\sqrt{80} = \sqrt{16*5} = 4\sqrt{5} ........(1)

\sqrt{125} = \sqrt{25*5} = 5\sqrt{5} .......(2)

Thus 4\sqrt{5} + 5\sqrt{5} = 9\sqrt{5}

Thus answer is A
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Re: Root(80)+root(125) [#permalink] New post 01 Oct 2012, 04:03
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Re: Root(80)+root(125) [#permalink] New post 01 Oct 2012, 18:42
Answer is A (Same explanation as Carcass's)
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Re: Root(80)+root(125) [#permalink] New post 04 Oct 2012, 12:59
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SOLUTION

\sqrt{80}+\sqrt{125} =

(A) 9\sqrt{5}
(B) 20\sqrt{5}
(C) 41\sqrt{5}
(D) \sqrt{205}
(E) 100

\sqrt{80}+\sqrt{125} =\sqrt{16*5}+\sqrt{25*5}=4\sqrt{5}+5\sqrt{5}=9\sqrt{5}.

Answer: A.

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Re: Root(80)+root(125) [#permalink] New post 05 Oct 2012, 03:46
.
sqt80=4sqrt5
sqrt125=5sqrt5

total = 9sqrt5
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Re: Root(80)+root(125) [#permalink] New post 06 Oct 2012, 09:24
\sqrt{80} + \sqrt{125}

\sqrt{2x2x2x2x5} + \sqrt{5x5x5}

4\sqrt{5} + 5\sqrt{5}

\sqrt{5} ( 4+5)

9\sqrt{5}

Ans: A
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Re: Root(80)+root(125) [#permalink] New post 18 Dec 2013, 13:04
Bunuel wrote:
\sqrt{80}+\sqrt{125} =

(A) 9\sqrt{5}
(B) 20\sqrt{5}
(C) 41\sqrt{5}
(D) \sqrt{205}
(E) 100

Practice Questions
Question: 52
Page: 159
Difficulty: 600



The only thing I know is that the answer is just under 24.. And it is definitely not D since D falls between 14 and 15.. And it's clearly not E. And out of the 3 left, B and C are waay too high above 24, and I figured sqrrt of 5 is around "2.something" so A made most sense.

Clearly this approach is very shaky but this time it worked.
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Root(80)+root(125) [#permalink] New post 20 Aug 2014, 22:32
\sqrt{80} is approx. 9 and \sqrt{125} is approx. 11 so the answer should be close to 20. Choice A is the closest.
Root(80)+root(125)   [#permalink] 20 Aug 2014, 22:32
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