J
:6. Solution.  On each roll of the wheel, you win ten dollars
if the ball falls in one of the 18 slots marked red and you lose
ten dollars - or "win" -10 dollars if the ball falls in one of
the 18 slots marked black or one of the 2 slots marked green. 
The amount won on a single bet is like one draw out of a box with
18 tickets marked 10, and 20 tickets marked -10.  In 100 spins,
your total winnings are like the sum of 100 draws from this box. <p>