Answer:
18.
Step-by-step explanation:
Central Limit Theorem
The Central Limit Theorem establishes that, for a normally distributed random variable X, with mean and standard deviation
, the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean
and standard deviation
.
For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.
For a proportion p in a sample of size n(n being at least 30), the sampling distribution of the sample proportion will be approximately normal with mean and standard deviation
In this question:
n has to be at least 30. So the choice that answer this question, a size of n too small to use a normal curve to approximate the sampling distribution, is 18.