Answer:
a) p=0.021
b) p=0.029
c) Exactly one audit: P=0.0965
More than one audit: P=0.0042
Step-by-step explanation:
a) If the income is less than $100,000, there is a probability of 21 in 1,000 of being audited. This is:

If the income is equal or more than $100,000, there is a probability of 29 in 1,000 of being audited. This is:

b) If we have 5 taxpayers with incomes under $100,000, and we want to know the probability that exactly one will be audited, we can model this a binomial randome variable, with p=0.021 and n=5:

There is a probability of 0.0965 that exactly one out of a sample of five taxpayers with incomes under $100,000 will be audited.
To calculate the probability that more than one will be audited, we use the same distribution:
![P(x>1)=1-[P(x=0)+P(x=1)]\\\\\\P(x=0) = \dbinom{5}{0} p^{0}q^{5}=1*1*0.8993=0.8993\\\\\\P(x=1) = \dbinom{5}{1} p^{1}q^{4}=5*0.021*0.9186=0.0965\\\\\\P(x>1)=1-[P(x=0)+P(x=1)]\\\\P(x>1)=1-(0.8993+0.0965)\\\\P(x>1)=1-0.9958\\\\P(x>1)=0.0042](https://tex.z-dn.net/?f=P%28x%3E1%29%3D1-%5BP%28x%3D0%29%2BP%28x%3D1%29%5D%5C%5C%5C%5C%5C%5CP%28x%3D0%29%20%3D%20%5Cdbinom%7B5%7D%7B0%7D%20p%5E%7B0%7Dq%5E%7B5%7D%3D1%2A1%2A0.8993%3D0.8993%5C%5C%5C%5C%5C%5CP%28x%3D1%29%20%3D%20%5Cdbinom%7B5%7D%7B1%7D%20p%5E%7B1%7Dq%5E%7B4%7D%3D5%2A0.021%2A0.9186%3D0.0965%5C%5C%5C%5C%5C%5CP%28x%3E1%29%3D1-%5BP%28x%3D0%29%2BP%28x%3D1%29%5D%5C%5C%5C%5CP%28x%3E1%29%3D1-%280.8993%2B0.0965%29%5C%5C%5C%5CP%28x%3E1%29%3D1-0.9958%5C%5C%5C%5CP%28x%3E1%29%3D0.0042)
There is a probability of 0.0042 that more than one out of a sample of five taxpayers with incomes under $100,000 will be audited.