Answer:
a) sample size ≥ 30
b) 0.0017
Step-by-step explanation:
a) The central limit theorem states that for population with mean μ and standard deviation σ and take sufficiently large random samples from the population. This will hold provided the sample size is sufficiently large (usually n > 30) for a normal population.
Therefore the sample size should be greater or equal to 30 i.e n ≥ 30.
b) Given that n = 45, μ = 11.4 minutes and σ = 3.2 minutes, the z score (z) is given by the equation:
[tex]z=\frac{x-\mu}{\frac{\sigma}{\sqrt{n} } }[/tex]
Substituting values to get:
[tex]z=\frac{x-\mu}{\frac{\sigma}{\sqrt{n} } }= \frac{10-11.4}{\frac{3.2}{\sqrt{45} } }=-2.93[/tex]
Using the z table:
P(x < 10) = P(z < -2.93) = 0.0017
the probability that a random sample of n=45 oil changes results in a sample mean time of less than 10 minutes is 0.0017
