Tyrion101 said:
The formula for the word problems is c=p-r cost and profit problems, and the formula is also usually something like x-.3x-85=85(.25) and I don't really understand how they get what seems to be an extra 85 in there. I think the reason I forgot these is because I just did it the way the book told me rather than figuring out why the extra number existed. How can you tell when you use a number more than once if it isn't obviously worded that way? Maybe it is and I'm just not seeing the forest through the trees.
This doesn't make any sense: c=p-r
The profit for any sort of business is revenue - costs, or P = R - C.
Revenue is the total money coming in, and costs represent the money being paid out. In simple examples, a company makes one kind of product, which it sells at a certain price, say $10. If it sells x items, the revenue would be R(x) = 10x ($).
Costs come from many things, but in a lot of these simple problems, there are two types of costs: fixed costs that are incurred no matter how many items are produced (mortgage payments, taxes, and so on), and variable costs that depend on how many items are produced (like wages for workers, electricity, and so on).
If the fixed cost is 1000 ($) and the items cost $7 each to make, the cost function would be C(x) = 1000 + 7x ($).
A typical problem is to find the break-even point, the production level at which the profit is 0. That means that the revenue equals the cost, so they set R(x) = C(x), or 10x = 7x + 1000.
Solving this equation, we get 3x = 1000, so x ≈ 333.3 items. If the company sells more than this number, it makes a profit. If it sells fewer than this, it loses money.
