The central issue for the players - to find and make a bet with a positive expected gain. But the players also need to know how to manage their money, ie how much to bet. On the stock markets (including the securities market), the problem is similar to this, but it is more complicated. The player, who is now an investor, looking for the "big profits at a manageable level of risk." In both these cases, we examine the use of the Kelly criterion that maximizes the expected value of the logarithm of income ("maximizes the expected logarithmic utility").