which situation is best modeled by an exponential distribution? suppose that, in a strand of dna, mutations occur randomly and independently of other mutations at an average rate of one mutation per 12,400 a. a geneticist is examining a strand of dna. what is the probability that she will observe a mutation within the next 15,000 a? suppose that defects in electrical wire occur randomly and independently of other defects. the average rate is 0.001 defects per cm of wire. what is the probability that a 100 m long spool of wire will contain fewer than two defects? suppose that a traffic light is green for 30 s, yellow for 4 s, and red for 56 s. if cars arrive at the intersection randomly, what is the probability a car will arrive when the light is yellow?