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Which of the following is closest to (4.2(1,590)/15.7)^(1/2) ?

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Which of the following is closest to (4.2(1,590)/15.7)^(1/2) ?  [#permalink]

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New post 25 Jun 2018, 05:59
12
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A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

88% (00:58) correct 12% (01:22) wrong based on 675 sessions

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Re: Which of the following is closest to (4.2(1,590)/15.7)^(1/2) ?  [#permalink]

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New post 25 Jun 2018, 06:09
2

Solution



To find:
• The value closest to the expression \(\sqrt{\frac{4.2(1,590)}{15.7}}\)

Approach and Working:
As we are trying to find out the closest value, we can approximate the given terms as follows:
    • 4.2 ~ 4
    • 1590 ~ 1600
    • 15.7 ~ 16

Therefore, we can rewrite the expression as \(\sqrt{\frac{4(1,600)}{16}}\) = \(\sqrt{4 * 100}\) = 20

Hence, the correct answer is option A.

Answer: A
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Re: Which of the following is closest to (4.2(1,590)/15.7)^(1/2) ?  [#permalink]

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New post 25 Jun 2018, 06:09
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Bunuel wrote:
Which of the following is closest to \(\sqrt{\frac{4.2(1,590)}{15.7}}\)?

A. 20

B. 40

C. 60

D. 80

E. 100


ALWAYS check the answer choices before solving the question!
When we do so, we see that the answer choices are VERY spread apart, which means we can save a ton of time by being super aggressive with our approximations (aka rounding)

So, we get: \(\sqrt{\frac{4.2(1,590)}{15.7}} ≈ \sqrt{\frac{4(1,600)}{16}}\)

\(≈ \sqrt{4(100)}\)

\(≈ \sqrt{400}\)

\(≈ 20\)

Answer: A

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Which of the following is closest to (4.2(1,590)/15.7)^(1/2) ?  [#permalink]

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New post 28 Jun 2018, 03:59
Bunuel wrote:
Which of the following is closest to \(\sqrt{\frac{4.2(1,590)}{15.7}}\)?

A. 20

B. 40

C. 60

D. 80

E. 100



NEW question from GMAT® Official Guide 2019


(PS10470)





4.2 ~ 4
1590~1600
15.7~16

\(\frac{4*1600}{16}\)
=\(\sqrt{(400)}\)
= 20

Thus the best answer is A.
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Re: Which of the following is closest to (4.2(1,590)/15.7)^(1/2) ?  [#permalink]

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New post 28 Jun 2018, 18:04
Bunuel wrote:
Which of the following is closest to \(\sqrt{\frac{4.2(1,590)}{15.7}}\)?

A. 20

B. 40

C. 60

D. 80

E. 100


First we can multiply the fraction by 10/10 and we have:

√[(42)(1,590)/157]

Approximating, we have:

√[(40)(1,600)/160]

√[(40)(10)] = √400 = 20

Answer: A
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Re: Which of the following is closest to (4.2(1,590)/15.7)^(1/2) ?   [#permalink] 28 Jun 2018, 18:04
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