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# The size of a certain population of bacteria doubles every 30 minutes

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Manager
Joined: 25 Sep 2018
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WE: Investment Banking (Investment Banking)
The size of a certain population of bacteria doubles every 30 minutes  [#permalink]

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08 Oct 2018, 11:15
1
00:00

Difficulty:

45% (medium)

Question Stats:

59% (01:07) correct 41% (01:16) wrong based on 32 sessions

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The size of a certain population of bacteria doubles every 30 minutes. After 2 hours of growth, the size of the population will be what percent greater than the size of the population 2 hours earlier?

A) 15 percent
B)16 percent
C)1,500 percent
D) 1,600 percent
E) 1,700 percent

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Re: The size of a certain population of bacteria doubles every 30 minutes  [#permalink]

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08 Oct 2018, 11:25
Abhi077 wrote:
The size of a certain population of bacteria doubles every 30 minutes. After 2 hours of growth, the size of the population will be what percent greater than the size of the population 2 hours earlier?

A) 15 percent
B)16 percent
C)1,500 percent
D) 1,600 percent
E) 1,700 percent

Say at the beginning it was x

Then at every 30 minutes interval it doubles.

1st 30 minutes 2*x
2nd 30 minutes 2*2*x
3rd 30 minutes interval 2*2*2*x
4th 30 minuts interval 2*2*2*2*x

In the form of 2^a for every 30 minutes.

Percentage increase (new-old)/old

16x-x = 15x/x = 15*100 = 1,500

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Re: The size of a certain population of bacteria doubles every 30 minutes  [#permalink]

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10 Oct 2018, 17:46
Abhi077 wrote:
The size of a certain population of bacteria doubles every 30 minutes. After 2 hours of growth, the size of the population will be what percent greater than the size of the population 2 hours earlier?

A) 15 percent
B)16 percent
C)1,500 percent
D) 1,600 percent
E) 1,700 percent

Let’s say the size now is 10. The size would be 20 after 30 minutes, 40 after 60 minutes, 80 after 90 minutes, and 160 after 120 minutes, or 2 hours.

We use the percent increase formula: (New - Old)/Old x 100. Thus, the percent increase is:

(160 - 10)/10 x 100 = 15 x 100 = 1,500 percent

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Re: The size of a certain population of bacteria doubles every 30 minutes   [#permalink] 10 Oct 2018, 17:46
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