Question

At the park, Joanne and Maria bought food and lemonade for themselves and their friend, Brian. Joanne bought 3 slices of pizza and 1 lemonade for $4.50. Maria bought 2 slices of pizza and 2 lemonades (one for her and one for Brian) for $4.00.
How much does Brian owe Maria for his lemonade?

Answer 1

let p = the cost of one pizza slice.
let l = the cost of one lemonade

So we have:
3p + 1l = 4.50
2p + 2l = 4.00

multiply the top equation by two
multiple the bottom equation by -1

6p + 2l = 9.00
-2p - 2l = -4.00

4p = 5.00
p= 1.25

Substitute 1.25 for p in the top equation.

3*1.25 +1l = 4.50
1l = 4.50 -3.75
l= .75

So one lemonade costs 75 cents.