Nuclear decay mcat question...help needed

[The_Juggernaut]

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I got this question correct but not sure why. Appreciate it if anybody can walk me through it. Thanks!

 

[deleted1077312]

You get the half life from the graph, then how many times do you divide 56/2 to get 14.
Twice, multiply that times the half life you got and that’s the answer

 

[The_Juggernaut]

Thanks!

 

[BerkReviewTeach]

This is a first order plot, where the half life is constant. If you look at the graph, 100% is at t=0, 50% is around t=53, 25% is around t=106, etc...

So the easy way to set this up is to say that 56 —> 28 —> 14, meaning it is cut in half TWICE. That requires two half lives, which is 2 x 53 = 106.

I hope this helps.