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

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Posts: 55271
Which of the following is closest to (4.2(1,590)/15.7)^(1/2) ?  [#permalink]

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25 Jun 2018, 05:59
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88% (00:58) correct 12% (01:22) wrong based on 675 sessions

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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)

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Joined: 04 Jan 2015
Posts: 2873
Re: Which of the following is closest to (4.2(1,590)/15.7)^(1/2) ?  [#permalink]

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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.

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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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25 Jun 2018, 06:09
Top Contributor
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: $$\sqrt{\frac{4.2(1,590)}{15.7}} ≈ \sqrt{\frac{4(1,600)}{16}}$$

$$≈ \sqrt{4(100)}$$

$$≈ \sqrt{400}$$

$$≈ 20$$

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

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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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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

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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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