Question

On Monday Joe bought 10 cups of coffee and 5 doughnuts for his office at the cost of $16.50. It turns out that the doughnuts were more popular than the coffee. On Tuesday he bought 5 cups of coffee and 10 doughnuts for a total of $14.25. Which equations could be used to determine the cost of the coffee?

Answer 1

Let x be the cost of a cup of coffee. On Monday, 10 cups of coffee cost 10x dollars, and 5 doughnuts cost 5y dollars. The total cost was $16.50, so we can write the equation:

10x + 5y = 16.50

On Tuesday, 5 cups of coffee cost 5x dollars, and 10 doughnuts cost 10y dollars. The total cost was $14.25, so we can write the equation:

5x + 10y = 14.25

We now have a system of two equations in two variables that we can solve to find the cost of a cup of coffee.