Question

Calculate a 90% confidence interval for the average age at which gifted children first count to 10 successfully. Choose the closest answer.

Answer 1

Solution:

Mean=30.69

n=36

SD=$\sigma=4.31$

SE$=\sigma/\sqrt n=4.31/\sqrt{36}=0.718$

90% CI value of z is 1.645.

So, z=1.645

So, CI$=(\mu\pm z\times SE)=(30.69\pm1.645\times0.718)$

Thus, CI$=(29.51,31.87)$