That means that on the average, that for every 8 times you lose 
money on a stock, there are 2 times when you earn money or break
even on a stock.

Therefore on the average, out of every 10 times when you invest 
in a stock, you lose money 8 of those times and you earn money or
break even on 2 of those times.

So the probability of losing money is 8 times out of 10, or 8/10
which reduces to 4/5.

Edwin