Question

Calculate the upper and lower limit for a 95% confidence interval about the mean.

A family wants to reduce its expenditures for personal items like gifts, newspapers, magazines and so forth. A sample of 49 months of receipts yields a mean of $220.00 with a standard deviation of $30.00. They decide to calculate a 95% confidence interval about this mean.

Standard error = (standard deviation)/(square root of sample size)

Upper limit (dollars and cents) _________

Lower limit (dollars and cents) _________

Answer 1

Upper limit (dollars and cents) $228.40
Lower limit (dollars and cents) $211.60

Answer 2

Need an explanation?

Answer 3

yeah i don't understand how to do this

Answer 4

Okay

Answer 5

Standard error = (standard deviation)/(square root of sample size) = 30/√49 = 30/7
1.96 * standard error = 1.96 * 30/7 = 8.4
Upper limit = mean + 1.96SE = 220 + 8.4
Lower limit = mean - 1.96SE = 220 - 8.4

Answer 6

ok i see now, thank you

Answer 7

Anytime :)