You are told that the time between calls to your company's customer service department follows an exponential distribution. You are also told that the probability that there is a call within the next 20 minutes is 0.40 . Ten minutes goes by and there is no call. Given this, what is the probability that there is a call within the next 20 minutes? a. 0.40 b. 0.20 c. 0.80 d. 0.30