A contractor involved in high
rise building construction
orders thousands of steel rods each year from
a supplier. The strength, X, of the rods is a normally distributed random variable. When a shipment
arrives, the contractor selects a random sample of 15 rods and determines the sample mean strength
and the s
ample standard deviation. These results are then used to compute a confidence interval for the
population mean strength of the rods.
For a particular shipment, the sample mean strength of the selected rods
990 pounds and the
sample standard deviation is
= 14.5 pounds. What is the margin of error for a 95% confidence
interval for the population mean strength? (Round your answer to 2 decimal places.)
tractor would like to have an interval that has a
margin of error than the one above.
Which of the following would contribute to accomplishing this goal? (Choose the most
Both decreasing the size of the sample mean
strength and increasing the size of the sample
to 30 rods would contribute to a reduction in the margin of error.
Increase the population mean strength.
Decrease the size of the sample mean strength.
Increase the size of the sample to 30 rods.
level of confidence to 99%
n 15, x 990 and s 14.5
value at the 95% level of significance is: 1.96
The margin of error is,
Margin Error E Z Critical