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

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

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New post 08 Oct 2018, 11:15
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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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New post 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

Answer choice C.

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

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New post 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

Answer: C
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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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