Solution to 1992 Problem 26

It appears that the line crosses through the point (35 \mbox{ min}, 200 \mbox{ counts/min}). It is also clear that if you continued the plotted line to the right of the graph, it would intersect the 100 \mbox{ counts/min} horizontal line somewhere between 40 \mbox{ min} and 45 \mbox{ min}. Therefore, the half-life must be between 5 \mbox{ min} and 10 \mbox{ min}. Therefore, (B) is the only answer that could possibly be correct.

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