A store is having a sale on 200 dvd movies. some of the movies are being sold for $10 and some are being sold for $12. if the store made $2200 after selling all 200 dvds, how many $12 dvds were sold?

X = $ 10 dvd's ... y = $ 12 dvd's

x + y = 200 ... x = 200 - y

10x + 12y = 2200

10 (200 - y) + 12y = 2200

2000 - 10y + 12y = 2200

-10y + 12y = 2200 - 2000

2y = 200

y = 200/2

y = 100 ... so there were 100 $ 12 dvd's sold