Question 1183155
this is asking what proportion of samples of 50 will have 7 or fewer customers who made a purchase?
that is asking what is the probability that with a 15% base rate 0.14 or fewer will make a purchase?
this is z=(0.14-0.15)/sqrt(0.15*0.85/50)
< -0.01/0.0505
< -0.1980
That probability is 0.4215
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Can use a normal approximation as a rough check.
mean is np=7.5
variance is np(1-p)=6.375
sd is sqrt (V)=2.525
and get a similar result.