EXAMPLE WORD QUESTION: Jack buys a candy bar for himself and his six friends, and a box of chocolates for his girlfriend, another box for his mother and another for his sister. He pays $25 in all. At another time he buys two candy bars for himself, but he buys boxes of chocolates as before and it costs him $20. How much is a candy bar and how much is a box of chocolates?
In dollars, x is the price of a candy bar and y is the price of a box of chocolates.
7x+3y=25 and 2x+3y=20.
Subtract one equation from the other: 5x=5, x=1. The price of a candy bar is $1.
Using either equation (we'll pick the second) 2x+3y=20 so 3y=20-2x. x=1 so:
3y=20-2=18, y=18/3=6. The price of a box of chocolates is $6.