In the biology lab of "Jefferson" high School ther

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swerve: Legendary Member; Posts: 2499; Joined: Sun Oct 29, 2017 2:04 pm; Followed by:6 members

In the biology lab of "Jefferson" high School ther

by swerve » Wed May 30, 2018 9:21 am

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In the biology lab of "Jefferson" High School, there are 5.4*10^6 germs, equally divided among 10,800 Petri dishes. How many germs live happily in a single dish?

A. 100
B. 200
C. 500
D. 1000
E. 5000

The OA is C.

Please, can anyone explain this PS question? I tried to solve it but I'm not sure about the correct answer. I need help. Thanks.

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Source: Beat The GMAT — Problem Solving | Wed May 30, 2018 9:21 am

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Sionainn@PrincetonReview: GMAT Instructor; Posts: 41; Joined: Mon Mar 12, 2018 9:54 am; Followed by:1 members

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by Sionainn@PrincetonReview » Wed May 30, 2018 11:16 am

Since we don't have a calculator and our time is tight we want to think about how we can manipulate these numbers in a way that minimizes calculations. We can rewrite the denominator as 10.8 x 10^3, so the whole thing can be rewritten as

$$\frac{5.4\times10^6}{10.8\times10^3}$$

Because we are multiplying we can split them into two separate fractions

$$\frac{5.4}{10.8}\times\frac{10^6}{10^3}$$

Simplify this to

$$\frac{1}{2}\times10^3$$

Which is equivalent to 0.5 x 10^3 or 500. So the answer is choice C.

Take care,
Sionainn $$$$

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by [email protected] » Wed May 30, 2018 2:51 pm

Hi swerve,

We're told that in the biology lab there are 5.4*10^6 germs, equally divided among 10,800 Petri dishes. We're asked for the number germs living in a single dish. The math behind this question can be done in a couple of different ways. Considering that the answer choices are 'spread out' and NOT in 'Scientific Notation', you might consider 'translating' the given numbers into non-Scientific Notation 'format.'

10^6 = 1,000,000 so we have (5.4)(1,000,000) germs

10,800 is a little more than 10,000, so we can 'round down' that number.

Thus, per dish, we have about :

(5.4)(1,000,000)/(10,000) =
(5.4)(100) =
about 540 germs per dish. There's only one answer that's close...

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8083; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Mon May 06, 2019 7:16 pm

swerve wrote:In the biology lab of "Jefferson" High School, there are 5.4*10^6 germs, equally divided among 10,800 Petri dishes. How many germs live happily in a single dish?

A. 100
B. 200
C. 500
D. 1000
E. 5000 .