On Tuesday last week, Leo dropped off 10 pairs of trousers and some shirts at Sudsy Laundry. He was given a bill of $140, charged at $5 per shirt and $9 for each pair of trousers. When he went to pick up his clothes yesterday, the attendant insisted that he had only dropped off 2 shirts. Leo reported the matter to the manager, who ordered the attendant to search for the rest of Leo's shirts. How many shirts were missing? Let's think first. Chain of thought:
The cost of laundering all of Leo's trousers is 10 * 9 = 90 dollars. Since the total bill was 140 dollars, this means that all the shirts were cleaned for 140 - 90 = 50 dollars. As each shirt is cleaned at 5 dollars, Sudsy Laundry therefore laundered a total of 50 / 5 = 10 shirts. The missing shirts are therefore 10 - 2 = 8 shirts.
Therefore, the answer is 8.