Problem I did not know how to do:

A student wants to measure the half life of a radioactive isotope. He is told the isotope has a half life of between 10 and 20 minutes. Illustrating your answers appropriate, describe:

A). the measurements that he should take

B). how he should use the measurements to arrive at an estimate of the half life for the isotope.

I understand that to measure the half life of a radioactive material you measure the activity of the sample at regular times.

What I do not understand is the significance of the half life being between 10 and 20 minutes.

I'm not sure how he should take the measurements?..

Does he measure the becquerel at various intervals and then plot this in the graph? If so, what is the significance of telling us that the half life is between 10 and 20 minutes? I know what a half life is but why is telling us this what the half life is in between any different from just measuring the becquerel on our own and figuring out the half life from that?