Sally "Knuckles" O'Realy loves motorbikes - she likes to mend them, ride them and pamper them. The young "smashing" biker-enthusiast wants to start a business in changing oil and filters for motorbikes. Demand is high and she wants her business to flourish. She decides that she will make fixed time slots of x minutes for clients, but how long should they be? She has heard from a very reliable source that time spent on oil change follows exponential distribtion with mean of 10 minutes (therefore ).

She wants to be sure that 95% of customer would be happy and served on time. What do you recommend Sally to set the time slot length to?