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Root of (16*20+8*32)=

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Re: Root of (16*20+8*32)=  [#permalink]

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New post 01 Nov 2015, 16:12
Hi EricImasogie,

While the major Radical rules won't show up too often on Test Day (you'll likely see just 1-2 questions that will involve radical rules), they are a standard part of the GMAT, so if you know the rules, then you should be able to pick up these points.

Since your 'assumptions' about how the math 'worked' were incorrect, I have a few questions about your studies so far:

1) How long have you been studying?
2) What resources have you been using?

It might be that you need some general 'math' practice before you do too much more GMAT practice.

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Re: Root of (16*20+8*32)=  [#permalink]

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New post 27 Mar 2016, 20:05
Here is a visual that should help.
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Screen Shot 2016-03-27 at 8.04.32 PM.png
Screen Shot 2016-03-27 at 8.04.32 PM.png [ 105.52 KiB | Viewed 894 times ]


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Re: Root of (16*20+8*32)=  [#permalink]

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New post 04 May 2016, 09:41
Bunuel wrote:
\(\sqrt{16*20+8*32}=\)

(A) \(4\sqrt{20}\)
(B) 24
(C) 25
(D) \(4\sqrt{20}+8\sqrt{2}\)
(E) 32



Solution:

We must first simplify the expression in the square root before actually taking the square root. In other words, we have to get the product of 16 and 20 and add it to the product of 8 and 32 before taking the square root.

√[(16)(20) + (8)(32)]

√(320 + 256)

√576 = 24

The answer is B.

Note: If struggling with determining the value of √576, we could have used the answer choices to our advantage. We need to ask ourselves what number, when squared, equals 576. Since we should have the value of 25^2 memorized, we would know that 25^2 = 625. Since 576 is slightly less than 625, we can reasonably determine that 24^2 = 576.
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Root of (16*20+8*32)=  [#permalink]

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New post 04 May 2016, 10:56
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ScottTargetTestPrep wrote:
Note: If struggling with determining the value of √576, we could have used the answer choices to our advantage. We need to ask ourselves what number, when squared, equals 576. Since we should have the value of 25^2 memorized, we would know that 25^2 = 625. Since 576 is slightly less than 625, we can reasonably determine that 24^2 = 576.


Just though about adding a line

\(\sqrt{576}\)

Check last digit is 6, the units digit can be 4 or 6

Check if any of the options having units digit 4 or 6, then apply the 25 rule, it can work wonders under exam hall situation...


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Root of (16*20+8*32)=  [#permalink]

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New post Updated on: 09 Jun 2016, 02:34
The first thing when you see such questions should be to simplify
16*20 + 8*32 = 320 + 256 = 576
Now, \(\sqrt{576}\)= 24

Correct Option: B

Originally posted by OptimusPrepJanielle on 08 Jun 2016, 20:42.
Last edited by OptimusPrepJanielle on 09 Jun 2016, 02:34, edited 1 time in total.
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Re: Root of (16*20+8*32)=  [#permalink]

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New post 08 Jun 2016, 22:11
Bunuel wrote:
\(\sqrt{16*20+8*32}=\)

(A) \(4\sqrt{20}\)
(B) 24
(C) 25
(D) \(4\sqrt{20}+8\sqrt{2}\)
(E) 32

Practice Questions
Question: 35
Page: 156
Difficulty: 600


\(\sqrt{16*20+8*32}=\)
\(\sqrt{16}=4
4 * [m]\sqrt{20+8*2}=\)
4 * \(\sqrt{36}=\)
4*6
24

B is the answer.
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Re: Root of (16*20+8*32)=  [#permalink]

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New post 25 Jul 2018, 16:34
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Re: Root of (16*20+8*32)= &nbs [#permalink] 25 Jul 2018, 16:34

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