Population problem

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Population problem

by shanice » Wed Aug 15, 2012 7:04 am
A certain population of bacteria doubles every 10 minutes.If the number of bacteria in the population initially was 10^4, what was the number in the population 1 hour later?

A)2(10^4)
B)6(10^4)
C)(2^6)(10^4)
D)(10^6)(10^4)
E)(10^4)6

Thank you in advance.

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by [email protected] » Wed Aug 15, 2012 7:11 am
shanice wrote:A certain population of bacteria doubles every 10 minutes.If the number of bacteria in the population initially was 10^4, what was the number in the population 1 hour later?
Population after 10 minutes = 2*(10^4) = (2^1)*(10^4)
Population after 20 minutes = 2*2*(10^4) = (2^2)*(10^4)
Population after 30 minutes = 2*2*2*(10^4) = (2^2)*(10^4)
...
Population after 60 minutes = = (2^6)*(10^4)

The correct answer is C.
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by GMATGuruNY » Wed Aug 15, 2012 7:44 am
shanice wrote:A certain population of bacteria doubles every 10 minutes.If the number of bacteria in the population initially was 10^4, what was the number in the population 1 hour later?

A)2(10^4)
B)6(10^4)
C)(2^6)(10^4)
D)(10^6)(10^4)
E)(10^4)6

Thank you in advance.
Since the population doubles every 10 minutes, in 60 minutes it will be multiplied by 2 six times:
10� * (2*2*2*2*2*2) = 2�10�.

The correct answer is C.
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by shanice » Wed Aug 15, 2012 10:12 am
C is the correct answer.

Thank you, guys.

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by shanice » Wed Aug 15, 2012 6:59 pm
To [email protected] & GMATGuruNY,

I understand your workings and the explanation for this problem but I have a doubt. When I read the question, the following sentence lead me to this understanding:-

"A certain population of bacteria doubles every 10 minutes".

So, I understood it as below:-

Time Population
Now 10^4
10 10^4 + 10^4 (Isn't doubling supposed to be this way?)
20


However, I couldn't solve the question because I got stuck with the computation. What's wrong with my understanding here?

I'm sorry for asking such a silly question but I really need to know.

Thank you, guys.

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by shanice » Thu Aug 16, 2012 10:08 pm
Can someone please reply me on this?

Thank you.

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by anuprajan5 » Thu Aug 16, 2012 10:29 pm
Shanice,

I think your confusion stems from the difference between double and multiply. If it was multiplying, then your logic works. Doubling is double a certain number.

Example - double 4 - 4*2
multiply 4 - 4*4

Regards
Anup