SOLUTION: Chelsea can buy 3 CDs and 3 cassette tapes for the same price as 4 video cassettes. She has enough money to buy 28 video cassettes. How many videos can she buy if she wants to buy

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Question 656228: Chelsea can buy 3 CDs and 3 cassette tapes for the same price as 4 video cassettes. She has enough money to buy 28 video cassettes. How many videos can she buy if she wants to buy and equal number of CDs, tapes, and videos if she spends all her money?
Unless I'm completely wrong 28 videos would equal 21 CDs and 21 cassette tapes (28v=21c+21t) but I can't figure out what to do from there (if I'm even on the right track)
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Call cost of 1 CD +x+
Call cost of 1 cassette tape +y+
Call cost of 1 video cassette +z+
given:
(1) +3x+%2B+3y+=+4z+
(2) +n%2Ax+%2B+n%2Ay+%2B+n%2Az+=+28z+
From (1)
(1) +x+%2B+y+=+%284%2F3%29%2Az+
From (2)
(2) +n+=+%2828z%29+%2F+%28+x+%2B+y+%2B+z+%29+
(2) +n+=+%2828z%29+%2F+%28%284%2F3%29%2Az+%2B+z+%29+
(2) +n+=+28+%2F+%287%2F3%29+
(2) +n+=+12+
She can buy 12 video cassettes
Hope I got it