You should have a table of the standard normal distribution.

Let , where is the time a punter spends in the casino in minutes, then has a standard normal distribution.

a) That corresponds to

If you have a table of the cumulative standard normal you can look up on that table to tell you but .

b) That corresponds to or

If you have a table of the cumulative standard normal you can look up on that table to tell you and to tell you , then

RonL