A used book store also started selling used CDs and videos. In the first week, the store sold a comb

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A used book store also started selling used CDs and videos. In the first week, the store sold a combination of 40 CDs and videos. They charged $4 per CD and $6 per video and the total sales were $180. Determine the total number of CDs and videos sold.

Let the number of cd's be c and number of videos be v. We're given two equations:

1. c + v = 40
2. 4c + 6v = 180

We can solve this system of equations using 3 methods:

• Substitution Method
• Elimination Method
• Cramer's Rule

No matter which method we choose, we get the same answer:
c = 30
v = 10