Three messenger services deliver to a small town in Oregon. Service A has 60% of all the scheduled deliveries, service B has 30%, and service C has the remaining 10%. Their on-time rates are 80%, 60%, and 40% respectively.
a. What proportion of the packages in the town are delivered on time?
e. What proportion of the packages in the town are delivered late?
Selected answer: a. 70% e. 30%
It seems i could just average the on time delivery rates to get the first answer. But that would be .6 and that's clearly the wrong answer.
To calculate, I could use a proportion formula.
a : b :: c : d ---> a/b=c/d