9. Bob and Mary went to the movies. Bob purchased 3 medium bags of popcorns and 2 large drinks and paid $11.00. Mary purchased 2 medium bags of popcorns and 4 large drinks and ended up paying $12.00. What was the price of a medium bag of popcorn and what was the price of a large drink? Denote p the price of a medium bag of popcorn and d the price of a large drink. Then we have 3 p + 2 d = 11 2 p + 4 d = 12
10. 3 p + 2 d = 11 2 p + 4 d = 12 -6 p - 4 d = -22 2 p + 4 d = 12 -4 p = -10 p = 2.50 Substituting back and solving for d we get d = 1.75. (multiply the first by -2) (add the first to the second) Medium bag of popcorn costs $2.50 and a large drink costs $1.75.
![Solving Linear Systems by the Substitution Method: ,[object Object]](https://image.slidesharecdn.com/solvinglinearsystemsbythesubstitutionmethod-110116134824-phpapp01/85/Solving-linear-systems-by-the-substitution-method-1-320.jpg)
![Solving Linear Systems by the Substitution ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)