can you slow down a whole mp3 track?

[Dave Sustaine]

can you slow down a whole mp3 track, eg set it to play at 70% of its regular speed so you can jam along until you get good enough for full speed. This is a big factor in me purchasing. thanks in advance for your help ...paul eg  say I want to jam along to hangar 18 by megadeth at 70% of the regular speed to practise the rhythm.