Video Explanation

Text Explanation

Let m = lemonades and let c = cookies

5m + 2c = 1.50

2m + 5c = 2.70

multiply top equation by 2

multiply bottom equation by –5

10m + 4c = 3

-10m + -25c = -13.50

-21c = -10.50

c = ½, or 50 cents

Plugging c back in to the first equation:

5m + 2(1/2) = 1.50

5m = .50

m = .10, or 10 cents

Therefore, together a lemonade and a cookie cost 60 cents. 

Alternatively, since this problem is looking for the value of (m + c), we can add the two initial equations together:

7m + 7c = 4.20

If we now factor out a 7 on the left:

7(m + c) = 4.20
7(m + c) / 7 = 4.20 / 7
(m + c) = .60