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Root(80)+root(125)

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Root(80)+root(125) [#permalink] New post 01 Oct 2012, 05:02
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Question Stats:

93% (01:30) correct 6% (00:16) wrong based on 92 sessions
\sqrt{80}+\sqrt{125} =

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

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Re: Root(80)+root(125) [#permalink] New post 01 Oct 2012, 05:03
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 01 Oct 2012, 07:43
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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 01 Oct 2012, 19:42
Answer is A (Same explanation as Carcass's)
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Re: Root(80)+root(125) [#permalink] New post 04 Oct 2012, 00:50
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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 04 Oct 2012, 13:59
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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NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

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COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!! ,11 Mixed Questions NEW!!!, 12 Fresh Meat NEW!!!

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!, 11 New DS set. NEW!!!


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Re: Root(80)+root(125) [#permalink] New post 05 Oct 2012, 04:46
.
sqt80=4sqrt5
sqrt125=5sqrt5

total = 9sqrt5
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Re: Root(80)+root(125) [#permalink] New post 06 Oct 2012, 10:24
\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] 06 Oct 2012, 10:24
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