a disc jockey must play 12 commercial spots during 1 hour of radio show. each commercial is either 30 or 60 seconds long. if the total commercial time during 1 hour is 8 minutes, how many 30 second commercials were played that hour? how many 60 second commercials?

Question

anonymous · Answer

assume there were a 30-second commercials

assume there were b 60-second commercials

then:

a + b = 12

30*a + 60*b = 8*60

tidy up the second equation:

a + 2b = 16

use elimination (equation 2 - equation 1):

b = 4

substitute back in:

a = 8

so there were 8 30-second commercials

and there were 4 60-second commercials