McDonalds recently sold small soft drinks for 100 medium sof

McDonald\'s recently sold small soft drinks for $1.00, medium soft drinks for $1.15 and large soft drinks for $1.30. During a lunch-time rush, Chris sold 40 soft drinks for a total of $45.25. The number of small and large drinks combined, was 10 fewer than the number of medium-sized drinks. How many large sized drinks were sold? (Choose to use 3 variables and 3 equations)

Solution

s + m + L = 40

s*1 + m*1.15 + L*1.30 = 45.25

s + L = m - 10

s - m + L = -10

adding eq 1 and eq 3

2*(s + L) = 30

s + L = 15

So, using equation 1

s + L + m = 40

15 + m = 40

m = 25

medium size drinks were 25

now

s + L = 15

s*1 + L*1.3 + 25*1.15 = 45.25

s + 1.3L = 16.5

subtracting both equations:

0.3 L = 1.5

L = 5

s = 10

Total large drinks sold = 5