Question 847193
The key word is that the arrivals are INDEPENDENT. Normally in order to find P(AB), we must find P(A) * P(B|A). But notice that since they are independent, A doesn't affect the outcome of B. Thus we can just multiply the resulting probabilities as is. This is very handy because the probability of 4 emergencies is P[emergency]^4 = .646^4 = .1742