Aweb 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 4.1 mb. yesterday, there were 1010 downloads of the song, for a total download size of 2761 mb. how many downloads of the high-quality version were there?

If the number of downloads of the standard version is x, and the high quality is x, 2.1*x+4.1*y=2761 (not 1010 due to that this is multiplied by 2.1 and 4.1, therefore representing the total amount of megabytes) In addition, there are 1010 total downloads, and it's either 2.1 MB or 4.1 MB, so x+y=1010.

We have 
2.1x+4.1y=2761
x+y=1010

Multiplying the second equation by -2.1 and adding it to the first equation, we get 2y=2761-1010*2.1=640 and by dividing both sides by 2 we get y=320 downloads of the high quality version

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