There are 233 feet of wood that are required, but we can only buy in lengths of 11 feet. Therefore, we have to take the ceiling of the division 233/11 because if you take less than what you need, you won't have enough, but if you take more than you need, but only the bare minimum of it, you will have enough without wasting money. Therefore, 233/11 = 21, but you have that extra couple feet left, so you need to buy an extra plank to get 22 planks of wood.
