Math
posted by Anonymous on .
a disc jockey must play 14 commercial spots during 1 hour of a radio show.Each commercial is either 30 seconds or 60 seconds long. If the total commercial time during 1 hour is 11 min, how many 30second commercials were played that hour. How many 60second commercials.

11 min * 60 s/min = 660 s,
x  30 s comm,
y  60 s comm,
x + y = 14 comm,
y = 14  x,
30x + 60y = 660 s,
Substitute 14  x for y:
30x + 60(14  x) = 660,
30x + 840  60x = 660,
60x = 660  840
30x = 180,
x = 6 30 s comm,
6 + y = 14,
y = 8 60 s comm.