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Population growth rate

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Population growth rate

by gmattesttaker2 » Fri Feb 21, 2014 11:56 pm
Hello,

Can you please tell me how to solve this:

In a certain country, a person is born every 3 seconds and a person dies every l0 seconds. Therefore, the birth and death rates account for a population growth rate of one person every:

A) 3 1/3 sec
B) 4 2/7 sec
C) 7 sec
D) 11 2/3 sec
E) 13 sec

OA: B
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by Uva@90 » Sat Feb 22, 2014 1:29 am
gmattesttaker2 wrote:Hello,

Can you please tell me how to solve this:

In a certain country, a person is born every 3 seconds and a person dies every l0 seconds. Therefore, the birth and death rates account for a population growth rate of one person every:

A) 3 1/3 sec
B) 4 2/7 sec
C) 7 sec
D) 11 2/3 sec
E) 13 sec

OA: B
Sri,
A person is born every 3 seconds
So for a second, 1/3
A person dies every 10 seconds
So, for a second ,1/10
Population growth rate is
1/3-1/10 = 7/30 per second.

But what question ask for is per person,
So ans is 30/7

Hence Ans is B

Regards,
Uva.
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by GMATGuruNY » Sat Feb 22, 2014 3:27 am
gmattesttaker2 wrote:Hello,

Can you please tell me how to solve this:

In a certain country, a person is born every 3 seconds and a person dies every l0 seconds. Therefore, the birth and death rates account for a population growth rate of one person every:

A) 3 1/3 sec
B) 4 2/7 sec
C) 7 sec
D) 11 2/3 sec
E) 13 sec

OA: B
For the time, plug in the LCM of the two rates = 3*10 = 30 seconds.
Since a person is born every 3 seconds, the number of people born in 30 seconds = 30/3 = 10.
Since a person dies every 10 seconds, the number of people who die in 30 seconds = 30/10 = 3.
Net rate per 30 seconds = 10-3 = 7 people.
7 people per 30 seconds = 1 person per 30/7 seconds.

The correct answer is B.
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by Abhishek009 » Sun Feb 23, 2014 9:22 am
gmattesttaker2 wrote:Hello,

Can you please tell me how to solve this:

In a certain country, a person is born every 3 seconds and a person dies every l0 seconds. Therefore, the birth and death rates account for a population growth rate of one person every:

A) 3 1/3 sec
B) 4 2/7 sec
C) 7 sec
D) 11 2/3 sec
E) 13 sec

OA: B

In 30 seconds ( + ) 10 Persons are Born

In 30 seconds ( - ) 3 Persons die.
_________________________________

In 30 Seconds 7 Persons are born.
_________________________________

Thus in 30 seconds population increases by 7 new persons.

7 persons are born every 30 seconds

1 Person is born every 30/7 seconds => 4 & 2/7 Seconds..
Abhishek
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