The times to pop a 3.4-ounce bag of microwave popcorn without burning it are Normally distributed with a mean time of 140 seconds and a standard deviation of 20 seconds. A random sample of four bags is selected and the
mean time to pop the bags is recorded. Which of the following describes the sampling distribution of all possible
samples of size four?

This question is solved using the central limit theorem, giving an answer of:

Fourth option, approximately normal with mean of 140 seconds and standard deviation of 10 seconds.

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

For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.

Mean of 140, standard deviation of 20, sample of 4:

By the Central Limit Theorem, the distribution is approximately normal.

Mean is the same, of 140.

, thus:

Thus, the correct answer is:

Fourth option, approximately normal with mean of 140 seconds and standard deviation of 10 seconds.

For another example of the Central Limit Theorem, you can check

b is the correct answer