I don\'t know what ... means so i\'ll assume it\'s <=, if it\'s > then use the formula P(X>a) = 1- P(X<=a) The CDF of an exponential distribution of parameter L is F(x) = 1-e^(-Lx) for x>=0 and 0 otherwise The mean of an exponential distribution is 1/L 1 Solution I don\'t know what ... means so i\'ll assume it\'s <=, if it\'s > then use the formula P(X>a) = 1- P(X<=a) The CDF of an exponential distribution of parameter L is F(x) = 1-e^(-Lx) for x>=0 and 0 otherwise The mean of an exponential distribution is 1/L 1.