A clothing company has designed a matching outfit of a pair of slacks and a shirt to go with it. The two items can be purchased together as a set or separately. They predict that 60% of buyers will buy the set together, 30% will buy only the shirt, and 10% will buy only the slacks. They have decided that they are going to produce 9,000 of the shirts. They are trying to decide how many pairs of the slacks they should produce in order best to meet the proportional demand for each item.

How many they should produce.

How can they calculate that number correctly? Explain how you determined your answer in the box below.