My Solution::
b i) no answer
b ii) no answer
b iii) no answer
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