Model Contexts with Two Variable Expressions Q3

Question

Katherine is a songwriter who collects royalties on her songs whenever they are played in a commercial or a movie. Katherine will earn $40 every time one of her songs is played in a commercial and she will earn $90 every time one of her songs is played in a movie. Katherine earned a total of $720 in royalties on 13 commercials and movies. Algebraically determine the number of commercials and the number of movies on which Katherine's songs were played.

Answer 1

Let C = # of commercial plays and M = # of movie plays

C + M = 13

4C + 9M = 72 (Divide by 10 before even writing the equation!)

Multiply the 1st equation by 4 and subtract it from the 2nd equation to eliminate C: 5M = 20

You finish it from here...and check your answers in the original equation.