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A certain population of bacteria doubles in size every 5

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A certain population of bacteria doubles in size every 5 [#permalink]  11 Feb 2004, 14:51
A certain population of bacteria doubles in size every 5 minutes. If the population is 2 ├Ч 106 at 1:00pm then the population at 1:25pm the same day will be?

A 6.4 ├Ч 106
B 12 ├Ч 106
C 6.4 ├Ч 107
D 2 ├Ч 1012
E 64 ├Ч 1012

Vivek.
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how did u get that.. my guess is between D or E..??
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shubhangi

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where did you get this question. I get
64 * 106. I think there is a typo in the answer. It should be A with the decimal point removed.
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anandnk wrote:
where did you get this question. I get
64 * 106. I think there is a typo in the answer. It should be A with the decimal point removed.

You are correct!
Either A) with out the decemal
or C) with 10^7
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64*10^6 is equiavalent to 6.4 * 10^7..

Since 64*10^6 is not among the answers...we obviously have to go for C i.e 6.4 * 10^7.

Have I cleared the confusion?

Vivek.
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"Start By Doing What Is Necessary ,Then What Is Possible & Suddenly You Will Realise That You Are Doing The Impossible"

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could someone show me the working??
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shubhangi

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2 * 106 = 212

After 5 mins 424
After 10 mins 848
After 15 mins 1696
After 20 mins 3392
After 25 mins 6784 = 64 * 106

Another way to do is 25/5 = 5 So at the end of 25 minutes
we will have 212 * 2^5 bacteria.

This is a small number of bacteria. I have a feeling that the original count must be 2^106 instead of 2 * 106
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Everytime the population is double, you multiply by 2
Since there is 5 times 5 minutes in 25 minutes, then the population doubles 5 times or 2^5
Then 2^5 * 2 * 10^6 = 2^6 * 10^6 = 64 * 10^6 = 6.4 * 10*7
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Paul

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i did the same way as u did Anand.. but wonder where i went wrong..
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shubhangi

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I think Vivek omitted to put the sign "^" for exponent...
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Paul

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