Answer:
190
Step-by-step explanation:
Data provided in the question:
Confidence level = 99%
Therefore,
α = 1% = 0.01
[ from standard normal table ]
z-value for = 2.58
Margin of error, E = $0.06
Standard deviation, σ = $0.32
Now,
n =
Here,
n is the sample size (or the minimum number of gas stations )
on substituting the respective values, we get
=
=
= 13.76²
= 189.3376 ≈ 190
Hence,
minimum number of gas stations that she should include in her sample is 190