Which of the following statements are correct?

1.A normal distribution is any distribution that is not unusual.
2.The graph of a normal distribution is bell-shaped.
3.If a population has a normal distribution, the mean and the median are not equal.
4.The graph of a normal distribution is symmetric.

2 and 4 are correct.

To determine which of the statements are correct, let's go through each statement one by one:

1. "A normal distribution is any distribution that is not unusual."
This statement is not correct. A normal distribution is a specific type of probability distribution characterized by a bell-shaped curve. It is not simply defined as anything that is not unusual. In statistics, a distribution is considered normal if its data points cluster around the mean in a symmetrical manner.

2. "The graph of a normal distribution is bell-shaped."
This statement is correct. The graph of a normal distribution indeed has a bell-shaped curve. It is symmetric around its mean, with the highest point at the mean.

3. "If a population has a normal distribution, the mean and the median are not equal."
This statement is not correct. In a normal distribution, the mean and the median are equal. This is one of the defining characteristics of a normal distribution. The mean is the arithmetic average of the data, while the median is the middle value. In a normal distribution, these two measures of central tendency are the same.

4. "The graph of a normal distribution is symmetric."
This statement is correct. As mentioned earlier, the graph of a normal distribution is indeed symmetric. It means that if you were to draw a vertical line at the mean, the curve on either side of the line would be mirror images of one another.

In summary, the correct statements are:
- The graph of a normal distribution is bell-shaped.
- The graph of a normal distribution is symmetric.