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If in a certain population, people are born at an average rate of 9 pe

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If in a certain population, people are born at an average rate of 9 pe  [#permalink]

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New post 16 Apr 2017, 23:47
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Question Stats:

73% (01:49) correct 27% (02:08) wrong based on 128 sessions

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If in a certain population, people are born at an average rate of 9 people every 2 seconds and people die at an average rate of 3 people every 2 seconds, by approximately how many people does the population increase in 1 day?

A. 17,280
B. 25,920
C. 129,600
D. 259,200
E. 388,800

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Re: If in a certain population, people are born at an average rate of 9 pe  [#permalink]

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New post 17 Apr 2017, 06:15
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In every 2 seconds, 9 people are born and 3 die. Hence, about 6 are added.
A day has 24 hours or
(24×3600)/2 2 second intervals.
Total people added in a day are 259200(Option D)

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Re: If in a certain population, people are born at an average rate of 9 pe  [#permalink]

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New post 17 Apr 2017, 06:29
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Option D

Change in population every 2 seconds = 9 - 3 = +6.

Total change in 24 hours (24*60*60) = 24*60*60*3/2 =.....200
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If in a certain population, people are born at an average rate of 9 pe  [#permalink]

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New post 19 Aug 2018, 10:04
Bunuel wrote:
If in a certain population, people are born at an average rate of 9 people every 2 seconds and people die at an average rate of 3 people every 2 seconds, by approximately how many people does the population increase in 1 day?

A. 17,280
B. 25,920
C. 129,600
D. 259,200
E. 388,800

If 9 people are born and 3 people die every 2 seconds, then the rate of increase is (9-3)= 6 people every 2 seconds, \(\frac{6p}{2secs}=\frac{3p}{1sec}\)

Population increase in one day

\(\frac{3p}{1sec}*\frac{60secs}{1min}*\frac{60mins}{1hr}*\frac{24hrs}{1day}=\frac{259,200p}{1day}\)

In one day: 259,200 people

For the arithmetic in the numerator, estimating and using the doubling/halving trick is easier

\((3*60*60*24)\approx(75*3,600)\)
\(=(150*1,800)=(300*900)=270,000\)


Answers are far apart. Only one answer is close to 270,000:

259,200
Answer D

*This explanation of how to do conversion problems by canceling units is excellent.
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Re: If in a certain population, people are born at an average rate of 9 pe  [#permalink]

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New post 19 Sep 2018, 12:22
Bunuel wrote:
If in a certain population, people are born at an average rate of 9 people every 2 seconds and people die at an average rate of 3 people every 2 seconds, by approximately how many people does the population increase in 1 day?

A. 17,280
B. 25,920
C. 129,600
D. 259,200
E. 388,800



the above information gives 6 people are born every 2 seonds or 3 people every 1 second, that means we get the below calculation

3*60*60*24=259200 option D
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Re: If in a certain population, people are born at an average rate of 9 pe   [#permalink] 19 Sep 2018, 12:22
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