Question

With 90% confidence, for sample mean 319.50, sample standard deviation 11.50, and sample size 35, what is the upper confidence limit with 2 decimal places?

Answer 1

Sample mean =

Sample standard deviation = s = 11.50

n = sample size = 35

Confidence level = c = 0.90

alpha = 1 - c = 1 - 0.90

Upper limit

Where tc is t critical value for degrees of freedom = n- 1 = 35 - 1 = 34 and alpha = 0.1

tc from excel using command:

= T.INV.2T(0.1,34)

= 1.691                (Round to 3 decimal)

UL = 319.50 + 3.287058             

UL = 322.79                      (Round to 2 decimal)

Upper limit of confidence interval = 322.79