Question

I Don't Know!!!

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.
I kind of need to know how to solve. I have more q's like this but if I know how to, I might be able to do it.

Answer 1

They sold 10 videos and 30 CDs

Explanation:

So, you need two different equations-

We will use c to represent CDs and v to represent videos

So-

c + v = 40

4c + 6v = 180

Single out a variable in the first equation-

v = 40 - c

Because this is equal to v, insert it where v is in the second equation-

4c + 6(40 - c) = 180

Multiply-

4c + 240 - 6c = 180

Solve-

-2c + 240 = 180

-2c = -60

c = 30

Now that you know c, use first equation to find v-

30 + v = 40

v = 10

So c = 30 and v = 10