The radioactive element americium has a half-life of 432 years. Suppose we start with a 20-g mass of americium.
How much will be left after 367 years?
A. 17.0 g
B. 11.1 g
C. 15.5 g
D. 8.8 g
E. 18.0 g
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Radioactive - Tougher problem
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is the OA B? If so, I can explain....charlie33 wrote:The radioactive element americium has a half-life of 432 years. Suppose we start with a 20-g mass of americium.
How much will be left after 367 years?
A. 17.0 g
B. 11.1 g
C. 15.5 g
D. 8.8 g
E. 18.0 g
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ssmiles08
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Is there some sort of formula for these kind of problems? It would be nice to know some solid way of going about this.
I would have just approximated 11.1 as the answer b/c you know in 432 years, the radioactive element would be 10g.
367 years a little more than 80% of 432 years which means it would have decayed about 80% of its first half life. 80% of 10 = 8 so 20 - 8 ~ 12
would have guesstimated it around 11-12% which would be B in this case.
I would have just approximated 11.1 as the answer b/c you know in 432 years, the radioactive element would be 10g.
367 years a little more than 80% of 432 years which means it would have decayed about 80% of its first half life. 80% of 10 = 8 so 20 - 8 ~ 12
would have guesstimated it around 11-12% which would be B in this case.
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Ian Stewart
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You'll never see a question like this on a real GMAT, first because you'd need to know what 'half-life' means, which is not something you're assumed to know on the GMAT (it's not a physics test), and second because the calculation is impossible without a calculator. Sure, you can tell from the answer choices which must be right, but if the GMAT were to design a question around this concept, they would not use numbers like 432 and 367 in the question; instead they'd use numbers that were manageable.
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Exactly.....Ian Stewart wrote:You'll never see a question like this on a real GMAT, first because you'd need to know what 'half-life' means, which is not something you're assumed to know on the GMAT (it's not a physics test), and second because the calculation is impossible without a calculator. Sure, you can tell from the answer choices which must be right, but if the GMAT were to design a question around this concept, they would not use numbers like 432 and 367 in the question; instead they'd use numbers that were manageable.
