The time between successive arrivals of calls to emergency service is random variable which follows exponential distribution. It was observed that on average calls arrive to emergency service every five minutes (1" i=5min) and average number of calls in one minute is a. The probability that the time between successive calls is less than 10 minutes is b. The probability that the time between successive calls is more than 5 minutes is c. The probability that the time between successive calls is between 10 and 15 minutes is