The Clean Pool company maintains residential swimming pools for customers in a city in Florida. Clean Pool has a regular maintenance schedule for all pools but also provides emergency service for customers requiring immediate help.

For emergency repairs, Clean Pool has contract workers who are assigned 12 specific pools to be on call for. One such worker is Jaime who is assigned 12 specific pools in his neighbourhood; in case of a call, he would have to repair them as soon as he could. It has been found that each of these pools require emergency repair approximately once every 40 days (assume Poisson arrivals) and that repair takes of a day.

Jaime finds this arrangement to be stress free, except when a customer calls with an emergency and Jaime can not help them immediately (i.e., he is working on another call at the time). How often does this happen (i.e., where a customer has to wait)?

Express your answer in PERCENTAGE % (i.e., if the answer is 39%, write 39, not 0.39; No need to add the "%" sign)