The customers arrive at store with exponentially distributed interarrival times with a mean of 30 minutes. What is the probability that interarrival time between two successive customers is 2 hours or more?
My attempt: 2 customers arrive every hour, therefore λ=2.
P(T≥2)=∫ λ^(-λt) dt ( where $λ=2$, upperbound is infinity, and lowerbound is 2).This gives an answer of=$0.018$
however the answer in the answer key is $0.18$ can someone tell me what I did wrong. Thank you very much