[AS2] Percentage based random choice

Ok so lets say I have a multi-dimension array with this data

[ [“Attack 1”, 60], [“Attack 2”, 20], [“Attack 3”, 15], [“Attack 4”, 5] ]

ok so the first part of the 2nd dimension array is the label for an attack frame in a movieclip while the 2nd number is a percentage of that one being picked.

What would be a good formula for choosing one of those attacks based on their arrays?

Just to make it a little bit clearer, “Attack 1” for instance has a 60 just to stand for 60%, i need a formula that uses that 60 to form said percentage