Size of albums

Hi,
I've got a problem with my itunes.
I've put 1985 songs on to itunes so far, yet the size is showing as 74.79 GB.
Looking at the albums I've put on each song has a huge size.

This seems strange as someone else I know has 2600 songs and that takes up 20 GB approx.

Can someone help with this ?

Cheers

What format are the songs in?
It's supposed to be MP3, which is for a normal 3,5 minute song at 256 kb/s around 5,5 mb in size.

You may know this and if you do disregard it, but you can navigate to home/music/itunes/itunes music/pick an artist/pick an album/pick a song.