Under the null p=1/2p = 1/2p=1/2, compare P(15 of 20 smokers die first)P(\text{15 of 20 smokers die first})P(15 of 20 smokers die first) vs.\ P(12 of 20)P(\text{12 of 20})P(12 of 20).
=1=1=1
<1<1<1
>1>1>1
Insufficient info.
