The time to complete a standardized exam is approximately normal with a mean of 70 minutes and a standard deviation of 10 minutes. How much time should be given to complete the exam so that 90% of the students complete the exam in the allotted time?

Question

The time to complete a standardized exam is approximately normal with a mean of 70 minutes and a standard deviation of 10 minutes.  How much time should be given to complete the exam so that 90% of the students complete the exam in the allotted time?

anonymous · Answer

I understand that its a Probability Distribution problem, but I dont know which formula(s) to use to figure this out

tkhunny · Answer

M  the proper number of minutes to meat the criterion.

$(M-70)/10  = Z_{90}$

Find the Z-value with 10% of the Normal Distribution in the right tail.  Solve for M.

anonymous · Answer

You are awesome.  Thank you.