Question

The time required to finish a test is normally distributed with a mean of 60 minutes and a standard
deviation of 10 minutes. What is the probability that a student will finish the test in less than 70 minutes?

Answer 1

Lets look at our normal distribution curve:

Answer 2

70 minutes is one standard deviation above the mean. So you want the sum of the percentages between negative infinity and 1 standard deviation above the mean.

Answer 3

take the Z-score of 70. find the distribution of the percentage of the score. Than compare it to the standard distributionstable of Z scores.

\[z = \frac{ 70 - 60 }{ \sigma } \]

your z score is 1 so the percentage from the table of distribution .84134.

you can look at the table yourself.

http://www.stat.tamu.edu/~lzhou/stat302/standardnormaltable.pdf

Answer 4

the percentage is 84.1 % I think....

Answer 5

Thank you guys!