Probability
posted by Nathan on .
The time required for a citizen to complete the 2000 U.S. Census "Long" form is normally distributed with a mean of 40 minutes and a standard deviation of 10 minutes. what proportion of the citizens will require less than 1 hour?

97.72%
Use the tool at
http://psych.colorado.edu/~mcclella/java/normal/accurateNormal.html 
Is there anyway you could explain that to me so I can understand it?

1 hour is 20 minutes = 2 standard deviations away from the mean. Your stats book should have a cumulative normal distribution table. Look up 2.0 in the table. I get .9772. Ergo, 97.72% will require less than an hour.