Using the condition for the hypothesis test of a proportion, it is found that since there are at least 10 successes and 10 failures in the sample, it is sufficient for him to use a simple random sample of 189 cars.
To test an hypothesis involving a proportion p in a sample of size n, it is needed that there are at least 10 successes and 10 failures, that is, these following conditions are needed.
In this problem:
Then:
[tex]np = 189(0.06) = 11.34 \geq 10[/tex]
[tex]n(1 - p) = 189(0.94) = 177.66 \geq 10[/tex]
Hence, since there are at least 10 successes and 10 failures in the sample, it is sufficient for him to use a simple random sample of 189 cars.
A similar problem is given at https://brainly.com/question/24261244