brain teasing mcat question

[podyon18]

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Suppose the half-life of 14C (currently 5730 years) has doubled in the last 50,000 years. When calculating the age of a specimen, if the changing rate is not taken into account, how will the calculated age compare to the actual age?

A)

The calculated age will be greater than the actual age because less 14C is present than there would be if the half-life had not changed
B)
The calculated age will be greater than the actual age because more 14C is present than there would be if the half-life had not changed
C)
The calculated age will be less than the actual age because less 14C is present than there would be if the half-life had not changed
D)

The calculated age will be less than the actual age because more 14C is present
than there would be if the half-life had not changed




Answer: A

 

[MedPR]

Do you have a question about this?

 

[gettheleadout]

Yeah, this was the MCAT Question of the Day today.

I got it right. 😎

But yeah, like MedPR said, is there a question here?

 

[sotto voce]

Suppose the half-life of 14C (currently 5730 years) has doubled in the last 50,000 years. When calculating the age of a specimen, if the changing rate is not taken into account, how will the calculated age compare to the actual age?

A)

The calculated age will be greater than the actual age because less 14C is present than there would be if the half-life had not changed
B)
The calculated age will be greater than the actual age because more 14C is present than there would be if the half-life had not changed
C)
The calculated age will be less than the actual age because less 14C is present than there would be if the half-life had not changed
D)

The calculated age will be less than the actual age because more 14C is present
than there would be if the half-life had not changed




Answer: A

A? Really?

The rate of decay has slowed down (the half-life has gone up), so there will be more left than there would be otherwise. Right?

And that means the age would be underestimated, since it would appear that not much has decayed, i.e., that not that much time has passed. That makes the answer D.

What am I missing?

Edit: A is correct. I read it as the half-life started at 5730 and then doubled. In fact, it doubled to 5730. Touche. 🙂

 

[podyon18]

No question - just thought it was a twist on whats usually a much simpler topic that somebody may appreciate seeing!