You want to borrow three rock CDs from your friend. She loves math puzzles and she always makes you solve one before you can borrow her stuff. Here's the puzzle: Before you borrow three CDs, she will have 39 CDs. She will have half as many country CDs as rock CDs, and one-fourth as many soundtracks as country CDs. How many of each type of CD does she have after you borrow three rock CDs?

Rock CD's=21

Country CD's=12

Soundtrack CD's=3

Step-by-step explanation:

let

r= rock CD's

c = country CD's

s = soundtrack CD's

Total CD's=r + c + s =39

2c=r

c/4=s

2c+c+c/4=39

8c+4c+c=156

13c=156

c=12

Substitute c=12 into 2c=r

2c=r

3(12)=r

24=r

r=24

Substitute c=12 into c/4=s

c/4=s

12/4=s

3=s

s=3

Therefore, she has

c=12

s=3

r=24

before she borrowed you 3 rock CD's

Sha has

r=21

s=3

c=12

after you borrowed 3 rock CD's

450

step-by-step explanation:

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step-by-step explanation: