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Approximation

by RiyaR » Sat Sep 13, 2014 4:22 am
Of the following, which if closest to ?
(0.15*495)/9.97
(A) 7.5
(B) 15
(C) 75
(D) 150
(E) 750

These type of questions involve approximation of a certain kind. How do I ensure I pick the right answer?
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by GMATGuruNY » Sat Sep 13, 2014 4:58 am
RiyaR wrote:Of the following, which if closest to ?
(0.15*495)/9.97
(A) 7.5
(B) 15
(C) 75
(D) 150
(E) 750
Since the answer choices are spread out, our calculations do not have to be very precise.
Round 495 up to 500 and 9.97 up to 10, as follows:
(15/100 * 500)/10 = 75/10 = 7.5.

The correct answer is A.
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by Brent@GMATPrepNow » Sat Sep 13, 2014 7:01 am
RiyaR wrote:Of the following, which if closest to ?
(0.15*495)/9.97
(A) 7.5
(B) 15
(C) 75
(D) 150
(E) 750
As Mitch mentioned, the answer choices are spread out, so we can use some estimation. In fact, I'd say the answer choices a VERY SPREAD OUT, which means we can be SUPER lenient with our estimation.
So, another way to tackle the question is to recognize that 0.15 is close to 1/7, 495 is close to 490, and 9.97 s close to 10.
So, we get: (1/7)(490)/10 = 70/10 = 7
Answer choice A is the only answer choice close to 7, so it must be the correct answer.

This strategy and others are covered in our free video, "General GMAT Math Strategies": https://www.gmatprepnow.com/module/gener ... es?id=1111

Cheers,
Brent
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by Brent@GMATPrepNow » Sat Sep 13, 2014 7:02 am
Brent@GMATPrepNow wrote:
RiyaR wrote:Of the following, which if closest to ?
(0.15*495)/9.97
(A) 7.5
(B) 15
(C) 75
(D) 150
(E) 750
As Mitch mentioned, the answer choices are spread out, so we can use some estimation. In fact, I'd say the answer choices a VERY SPREAD OUT, which means we can be SUPER lenient with our estimation.
So, another way to tackle the question is to recognize that 0.15 is close to 1/7, 495 is close to 490, and 9.97 s close to 10.
So, we get: (1/7)(490)/10 = 70/10 = 7
Answer choice A is the only answer choice close to 7, so it must be the correct answer.

This strategy and others are covered in our free video, "General GMAT Math Strategies": https://www.gmatprepnow.com/module/gener ... es?id=1111

Cheers,
Brent
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by GMATinsight » Sun Sep 14, 2014 9:52 pm
RiyaR wrote:Of the following, which if closest to ?
(0.15*495)/9.97
(A) 7.5
(B) 15
(C) 75
(D) 150
(E) 750

These type of questions involve approximation of a certain kind. How do I ensure I pick the right answer?
The options are widely separated, therefore the approximation can be done quickly and easily

(0.15*495)/9.97 = (15/100) *500/10 = 7.5

Approximation of 9.97 = 10
Approximation of 495 = 500
Approximation of 0.15 = 15/100

Answer: Option A
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by [email protected] » Sun Sep 14, 2014 10:24 pm
Hi RiyaR,

Each of the given explanations essentially explains the same thing, so I won't rehash any of that here.

I can tell you that the GMAT will ask you to perform at least 1 approximation during the Quant section (it's a built in "skill test" that is a part of every Test Taker's exam). Beyond that, you should be ready to use the answer choices to your advantage. When the answers are properly "spaced out", as they are in this prompt, you have an opportunity to save time by NOT performing the exact calculation that is given. Be on the lookout for these opportunities.

The exception to this rule is when the answer choices are "decimal shifted."

For example:
.02
.2
2
20
200

These types of questions are almost always based on PEMDAS rules, so you MUST perform the proper calculations, otherwise you'll be "off" by some factor of 10.

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