At a certain theater, the cost of each adults ticket is $5 and the cost of each childs ticket is $2. What is the average cost of all the adults and chilren's tickets sold at the theater yesterday?
1) yesterday the ratio of the number of childrens tickets sold at the theater to the number of adults tickets sold was 3 to 2
2) yesterday 80 adults tickets were sold at the theater
OA is A, but why?
Because they ask us "the average cost", so we don't need definite numbers, ratio is enough.