Question

A Web music store offers two versions of a popular song. The size of the standard version is 2.1 megabytes (MB). The size of the high-quality version is 4.2 MB. Yesterday, there were 1390 downloads of the song, for a total download size of 4683 MB. How many downloads of the high-quality version were there?

Answer 1

H=310

Explanation:

This problem is a great systems of equations problem--you have two different variables: song size and number of songs.

Let's call the number of standard version downloads (S) and the high quality downloads (H).

You can make two statements:

For number of songs downloaded: S + H = 910

For download size: 2.8(S) + 4.4(H) = 3044.

S will be the same number in both equations and H will be the same number in both equations, so to find S, we can rearrange the first statement to H = 910 - S, then substitute or plug in (910 - S) wherever you see an H in the second equation so that you have only S's in your equation. Should look like this:

2.8(S) + 4.4(910 - S) = 3044

2.8S + 4004 - 4.4S = 3044

-1.6S = -960

s = 600

Your question only asks for the standard version downloads, but to help you out in future Systems situations-

You can also solve for H once you have S by plugging it into either of your equations like this:

600 + H = 910

-600

Hope this helps!