Alice arrives at a bus stop at 2PM, to take R1 bus. R1 buses arrive at the bus stop as a Poisson process with rate 1/20 buses per minute. (So, the average interval between consecutive R1 buses is 20 min.) Bob arrives at the same bus stop at 2:30PM, to take R2 bus. R2 buses arrive at the bus stop as a Poisson process with rate 1/10 buses per minute. The R1 and R2 bus arrival processes are independent. What is the probability that Bob will take a bus before Alice