if a girl scout is selling cookies to people who randomly en

if a girl scout is selling cookies to people who randomly eneter a shopping mall, what is the probability that the next box sold will be peanut butter patties/tagalongs or peanut butter sandwhich/ do-si-dos?

Solution

It is not given that how many type of boxes are available in the store. So let us assume that there are only given two type of boxes in the store and both are equally likely to be sold. Let A shows the event that peanut butter patties/tagalongs will be sold and B shows the event that peanut butter sandwhich/ do-si-dos will be sold. Since both boxes are equally likely to be sold so we have

P(A)=P(B)=0.5

Therefore the probability that the next box sold will be peanut butter patties/tagalongs or peanut butter sandwhich/ do-si-dos is

P(A or B)= P(A)+P(B)=0.5+0.5=1