A simple random sample of 20 items resulted in a sample mean of 10. The population standard deviation is = 3. Round your answers to two decimal places. a. What is the standard error of the mean, ?
b. At 95% confidence, what is the margin of error?

a. 0.67

b. 1.31

Step-by-step explanation:

We have the following information n = 20, mean (m) = 10 and standard deviation (sd) = 3

a.

SE (m) = sd / n ^ (1/2)

replacing we have:

SE (m) = 3/20 ^ (1/2) = 0.67

Therefore the standard error of the mean is 0.67

b.

the critical value is obtained as shown below:

the level of sifnificance is alfa = 1 - 0.95 = 0.05

the critical value with level of significance alfa / 2 = 0.05 / 2 = 0.025

and to this value corresponds z = 1.96 (z table)

The margin of error with 95 confidence is calculated as follows:

E = z * SE

E = 1.96 * 0.67

E = 1.31

Therefore the margin of error is 1.31