Answer:
The answer is below
Step-by-step explanation:
A national standard requires that public bridges over 20 feet in length must be inspected and rated every 2 years. The rating scale ranges from 0 (poorest rating) to 9 (highest rating). A group of engineers used a probabilistic model to forecast the inspection ratings of all major bridges in a city. For the year 2020, the engineers forecast that 4%of all major bridges in that city will have ratings of 4 or below.
a. Use the forecast to find the probability that in a random sample of major bridges in the city, at least 3 will have an inspection rating of 4 or below in 2020.
Answer:
This problem is a probability binomial distribution and it can be solved using the formula:

Hence the solution to the problem is given as:
P(x ≥ 3) = 1 - P(x < 3) = 1 - [ P(x=0) + P(x=1) + P(x = 2)]
Given that p = 4% = 0.04, q = 1 - p = 1 - 0.04 = 0.96, n = 10. Hence:
![P(x=0)=C(10,0)*0.04^{0}*(0.96)^{10-0}=0.6648\\\\P(x=1)=C(10,1)*0.04^{1}*(0.96)^{10-1}=0.277\\\\P(x=2)=C(10,2)*0.04^{2}*(0.96)^{10-2}=0.0519\\\\P(x\geq 3)=1-[0.6648+0.277+0.0519]=0.0063](https://tex.z-dn.net/?f=P%28x%3D0%29%3DC%2810%2C0%29%2A0.04%5E%7B0%7D%2A%280.96%29%5E%7B10-0%7D%3D0.6648%5C%5C%5C%5CP%28x%3D1%29%3DC%2810%2C1%29%2A0.04%5E%7B1%7D%2A%280.96%29%5E%7B10-1%7D%3D0.277%5C%5C%5C%5CP%28x%3D2%29%3DC%2810%2C2%29%2A0.04%5E%7B2%7D%2A%280.96%29%5E%7B10-2%7D%3D0.0519%5C%5C%5C%5CP%28x%5Cgeq%203%29%3D1-%5B0.6648%2B0.277%2B0.0519%5D%3D0.0063)