Answer:
There were 300 standard version of songs downloaded at Web music store.
Step-by-step explanation:
Let the number of standard version of song download be 'x'.
Let the number of high-quality version of song download be 'y'.
Given:
Total songs downloaded = 780
Now we know that;
Total songs downloaded is equal to sum of the number of standard version of song download and the number of high-quality version of song download.
framing in equation form we get;
![x+y=780\ \ \ \ \ equation \ 1](https://tex.z-dn.net/?f=x%2By%3D780%5C%20%5C%20%5C%20%5C%20%5C%20equation%20%5C%201)
Also Given:
Size of standard version of song = 2.5 MB
Size of high-quality version of song = 4.7 MB
Total Download size = 3006 MB
Now we know that;
Total Download size is equal to sum of Size of standard version of song multiplied by the number of standard version of song download and Size of high-quality version of song multiplied by the number of high-quality version of song download.
framing in equation form we get;
![2.5x+4.7y =3006 \ \ \ \ equation \ 2](https://tex.z-dn.net/?f=2.5x%2B4.7y%20%3D3006%20%5C%20%5C%20%5C%20%5C%20equation%20%5C%202)
Now Multiplying equation 1 by 2.5 we get;
![2.5(x+y)=780\times 2.5\\\\2.5x+2.5y = 1950 \ \ \ \ equation \ 3](https://tex.z-dn.net/?f=2.5%28x%2By%29%3D780%5Ctimes%202.5%5C%5C%5C%5C2.5x%2B2.5y%20%3D%201950%20%5C%20%5C%20%5C%20%5C%20equation%20%5C%203)
Now Subtracting equation 3 from equation 2 we get;
![(2.5x+4.7y)-(2.5x+2.5y) =3006 - 1950\\\\2.5x+4.7y-2.5x-2.5y = 1056\\\\2.2y =1056\\\\y =\frac{1056}{2.2}=480](https://tex.z-dn.net/?f=%282.5x%2B4.7y%29-%282.5x%2B2.5y%29%20%3D3006%20-%201950%5C%5C%5C%5C2.5x%2B4.7y-2.5x-2.5y%20%3D%201056%5C%5C%5C%5C2.2y%20%3D1056%5C%5C%5C%5Cy%20%3D%5Cfrac%7B1056%7D%7B2.2%7D%3D480)
Substituting the value of y in equation 1 we get;
![x+y=780\\\\x+480=780\\\\x=780-480 = 300](https://tex.z-dn.net/?f=x%2By%3D780%5C%5C%5C%5Cx%2B480%3D780%5C%5C%5C%5Cx%3D780-480%20%3D%20300)
Hence there were 300 standard version of songs downloaded at Web music store.