check out the 'Kelly Criterion' -- a related topic.
Kelly criterion - Wikipedia, the free encyclopedia
Kelly Criterion % = W - [(1 - W) / R] = What % of capital to bet each time where;
W= Win % (Winning Trades / Total Trades)
R = Win/Loss Ratio (Expected Dollars Won When You Win vs Expected Dollars Lost When You Lose)
The optimum bet for the greatest growth of bankroll is making the full bet suggested by the Kelly criterion, but this produces a volatile result.