If the contestent won the $100 case then they would go home with $70.
You can sum up the $ amount that each case would give you times its relative probibility that it will be picked, in this case they all have the same probibility.
The resulting amount is what you can expect to leave with on average.
// Comment (Joe Romine) don't forget to divide by 5 after summing up the ammount that each case would give you (after taxes)
