How far do you need to run to train for a race?

I read an article today about the amount of mileage people should be running when training for various events. of course everyone is different and it depends on your goals. if you a want fast time in a 10km or you just want to finish the race, the amount of miles are going to vary quite considerably. I looked at the Marathon and for us mere mortals it suggests 30-50 miles a week. I have been doing about 17 to 25 with the odd 30 miles a week here and there. So I was pleased to read this. Then I looked on other sites and some people were saying anything from 20 to 100 miles a week. Not exactly a scientific study but I found it interesting none the less.

I think just staying injury free throughout training is key and not overdoing it. I find not overdoing it quite easy.

5K
Runner  Miles per week
Elite   70-80
Mortal  20-25

10K
Runner  Miles per week
Elite   80-100
Mortal  25-30

Half Marathon
Runner  Miles per week
Elite   100-110
Mortal  30-40

Marathon
Runner  Miles per week
Elite   100-140
Mortal  30-50