Let W be the exponentially distributed waiting time in minutes for the next metro train to arrive. If P (W < 2) = 1/3, compute P ( W >7| W?5). Solution Exponential distribution is memoryless, so we have: P(W > 7 | W > 5) = P(W > 7-5 | W > 0) = P(W > 2) = 1 - P(W < 2) = 1 - 1/3 = 2/3.