Assuming the population has an approximate normal distribution, if a sample of size $n=20$ has a sample mean $\bar{x}=15$ and sample standard deviation $s=3$ What is the degree of freedom?

Step 1 ：Given a sample size of \( n=20 \)

Step 2 ：Calculate the degree of freedom as \( n-1 \)

Step 3 ：Substitute the given value \( n=20 \) into the formula

Step 4 ：Degree of freedom \( = 20 - 1 \)

Step 5 ：Degree of freedom \( = 19 \)

Step 6 ：\( \boxed{19} \)