SOLUTION: a disc jockey must play 12 commercial spots during a 1 hour of radio.each commercial spot is either 30 seconds or 60 seconds. if the total commercial time is 1 hour 8 minutes, how

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: a disc jockey must play 12 commercial spots during a 1 hour of radio.each commercial spot is either 30 seconds or 60 seconds. if the total commercial time is 1 hour 8 minutes, how       Log On


   

Question 260497: a disc jockey must play 12 commercial spots during a 1 hour of radio.each commercial spot is either 30 seconds or 60 seconds. if the total commercial time is 1 hour 8 minutes, how many 30 second commercials are there?
Answer by drk(1908) About Me  (Show Source):
You can put this solution on YOUR website!
Let X = 30 sec and Y = 60 sec spots. Now 1 hr 8 min - 1 hr = 8 min = 480 seconds.
we get
(i) X+%2B+Y+=+12
(ii) 30X+%2B+60Y+=+480
step 1 - solve (i) for X to get
(iii) +X+=+12+-+Y
substitute (iii) into (ii) to get
(iv) 30%2812-Y%29+%2B+60Y+=+480
distribute to get
(v) 360+-+30Y+%2B+60Y+=+480
combine like terms to get
(vi) 30Y+=+120
Y = 4
X = 8
There are 8 - 30 second comercials