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# The half-life of a radioactive element is defined as the amount

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Joined: 25 Apr 2018
Posts: 637
GMAT 1: 680 Q49 V34
The half-life of a radioactive element is defined as the amount  [#permalink]

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04 Feb 2019, 08:42
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35% (medium)

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68% (01:33) correct 32% (01:37) wrong based on 37 sessions

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The half-life of a radioactive element is defined as the amount of time required for the amount of the element to decrease by half. If the half-life of an element is 3 years, how long will it take for the element to be reduced to one-eighth of its original amount?

A. 3 years

B. 9 years

C. 21 years

D. 24 years

E. 27 years

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Re: The half-life of a radioactive element is defined as the amount  [#permalink]

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04 Feb 2019, 09:15
I think this is a disguised population problem:

1 HL --> 50% or 1/2
2 HL --> 25% or 1/4
3 HL --> 12.5% or 1/8

If each half life is 3 years, then 3 HL = 9, B
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Re: The half-life of a radioactive element is defined as the amount  [#permalink]

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04 Feb 2019, 09:28
gmat1393 wrote:
The half-life of a radioactive element is defined as the amount of time required for the amount of the element to decrease by half. If the half-life of an element is 3 years, how long will it take for the element to be reduced to one-eighth of its original amount?

A. 3 years

B. 9 years

C. 21 years

D. 24 years

E. 27 years

1/2 in 3 years (given)

1/4 in 6 years

1/8 in 9 years

B
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Re: The half-life of a radioactive element is defined as the amount  [#permalink]

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06 Feb 2019, 20:07
gmat1393 wrote:
The half-life of a radioactive element is defined as the amount of time required for the amount of the element to decrease by half. If the half-life of an element is 3 years, how long will it take for the element to be reduced to one-eighth of its original amount?

A. 3 years

B. 9 years

C. 21 years

D. 24 years

E. 27 years

If the amount of the element starts at 1 gram, then after 3 years, it will be at 1/2 gram, then after 6 years it will be at 1/4 gram, and finally, after 9 years, it will be at 1/8 gram.

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Re: The half-life of a radioactive element is defined as the amount   [#permalink] 06 Feb 2019, 20:07
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