I would never do this sort of thing, never...ahem.

  

Here is a puzzle that is based on something i witnessed today...ahem ! I would never do something as silly as this. 

A man loaded 140lbs of sheep feed on to his trailer, and set off to feed some sheep. After travelling 4 miles on the road he found that 60lbs of the feed in the trailer had gradually spilled out of the sacks  ( what an idiot ) and was spread the entire length of this road. Knowing these facts, what percentage of the feed was spilled per mile of the journey travelled ?