Consider the question. John is a door-to-door salesman. He visits 50 houses a day. 20% of them buy something from them. Of those that buy something half buy a $50 set of knives and the other half buy a $150 set of knives. How much does he sell a week when he works 5 days a week?
 If the answer is '5000'; explain the reasoning:
There are 50 * .2 = 10 houses buying from him per day. Of those 10 / 2 = 5 buy each type of knife set. So he gets 5 * 50 = $250 per day from the cheap set. He also gets 5 * 150 = $750 from the expensive set. So he makes a total of 250 + 750 = $1000 per day. That means he makes 1000 * 5 = $5000.