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

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Math Expert
Joined: 02 Sep 2009
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If in a certain population, people are born at an average rate of 9 pe  [#permalink]

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16 Apr 2017, 22:47
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Difficulty:

25% (medium)

Question Stats:

73% (01:51) correct 27% (02:14) wrong based on 116 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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17 Apr 2017, 05:15
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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17 Apr 2017, 05:29
1
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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19 Aug 2018, 09:04
1
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

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

259,200

*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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19 Sep 2018, 11:22
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
Re: If in a certain population, people are born at an average rate of 9 pe &nbs [#permalink] 19 Sep 2018, 11:22
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