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 between 40 and 70 minutes?
Some one help!

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 between 40 and 70 minutes?
Some one help!

anonymous · Answer

Z score = ( 40 - 60 )/ 10 = - 2
Z score = ( 70 - 60) / 10 =  1
     P ( 40 < X < 70 ) 
=  P ( -1 < Z < 1 ) = ...

Look up your Z score table to get Probability

anonymous · Answer

@Stina_rox96 Can you continue?

kropot72 · Answer

The limits are -2 sigma and +1 sigma from the mean. The probability of being -2 sigma from the mean is 0.4773 and the probability of being +1 sigma from the mean is 0.3413.
What is the overall probability?

kropot72 · Answer

@Chlorophyll Please check your final equation.

anonymous · Answer

I mean =  P ( -2 < Z < 1 ) = ...

kropot72 · Answer

@Stina_rox96 You will get the same answer with either method. Mine relies on known properties of the Standard Normal Distribution Curve