An online shopping store receives customer queries through its helpdesk phoneline. The helpdesk manager hires an IMM graduate to collect and analyse its call logs. It is found that the rate at which customers call the phoneline follows a Poisson probability distribution. The graduate calculates that an average of 5 calls are received in a 20-minute period during the day. Calculate the probability of 2 or fewer calls being received in a 20 minute-period during the day. Show your working