TIME TO COMPLETE STANDARDIZED EXAM IS APPROXIMATELY NORMAL W

TIME TO COMPLETE STANDARDIZED EXAM IS APPROXIMATELY NORMAL WITH A MEAN OF 70 MINUTES AND STANDARD DEVIATION OF 10 MIN. USING THE 68-95-99.7 RULE, WHAT PERCENT OF STUDENTS WILL COMPLETE EXAM IN UNDER AN HOUR?

Solution

Normal Distribution
Mean ( u ) =70
Standard Deviation ( sd )=10
Normal Distribution = Z= X- u / sd ~ N(0,1)                  
P(X < 60) = (60-70)/10
= -10/10= -1
= P ( Z <-1) From Standard Normal Table
= 0.1587 ~ 15.87%