You could use a normal cdf - shouldn't be a huge problem. However, a lot of queueing problems assume a poisson distribution from memory.
sevay taken outside a resturant for wating time. mean in 45min and standard deviation is 12min.
determine the probability that a random person had to wait less that 20 min.
can I use normalcdf(0,20,45,12) to get the right answer?