Shoppers charged incorrectly 2 out of 30 times - what is the probability that the shopper will not be charged incorrectly if they purchase 12 items-
I am a math tutor and am having trouble with this problem - answer is .437

From the data the probability of being charged incorrecty for a purchase is 2/30 = 1/15. So the probability of not being charged incorrectly for a purchase is 1 - 1/15 = 14/15. Now, if the probability of something happening is p, to have that thing happen n times in a row is p^n. Here you have p=14/15 and n=12.