**Answer:**

The 95% confidence interval would be given by (18.73;23.07)

**Step-by-step explanation:**

Assuming these data

20 40 22 22 21 21 20 10 20 20

20 13 18 50 20 18 15 8 22 25

22 10 20 22 22 21 15 23 30 12

9 20 40 22 29 19 15 20 20 20

20 15 19 21 14 22 21 35 20 22

**Previous concepts **

A **confidence interval** is "a range of values that’s likely to include a population value with a certain degree of confidence. It is often expressed a % whereby a population means lies between an upper and lower interval".

The **margin of error** is the range of values below and above the sample statistic in a confidence interval.

**Normal distribution**, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

**Solution to the problem**

The confidence interval for the mean is given by the following formula:

(1)

First we need to find the sample mean with the following formula:

And in order to find the sample standard deviation we can use the following formula:

In order to calculate the critical value we need to find first the degrees of freedom, given by:

Since the Confidence is 0.95or 95%, the value of and , and we can use excel, a calculator or a table to find the critical value. The excel command would be: "=-T.INV(0.025,49)".And we see that

Now we have everything in order to replace into formula (1):

So on this case the 95% confidence interval would be given by (18.73;23.07)