A magnum bottle of champagne costs and contains 25 glasses of champagne. A group of girls bought one bottle, but gave away four glasses to the clingy boys close by. How much did that cost the girls?
In problems like this one, it is helpful to figure out the cost per unit, which in this case is the price of one glass of champagne. Then you can multiply that price by the glasses the girls gave away to find out how much they lost.
The price of one glass of champagne is
Then the price of four glasses is
Giving away four glasses of champagne cost the girls a total of $.