Minitab help with incorrect answers a b c ThanksSolutionNorm

Minitab help with incorrect answers a, b, c. Thanks

Solution

Normal Distribution
Mean ( u ) =10
Standard Deviation ( sd )=4
Normal Distribution = Z= X- u / sd ~ N(0,1)                  
a)
P(X > 8) = (8-10)/4
= -2/4 = -0.5
= P ( Z >-0.5) From Standard Normal Table
= 0.6915                  
P(X < = 8) = (1 - P(X > 8)
= 1 - 0.6915 = 0.3085                  
b)
P(X > 15) = (15-10)/4
= 5/4 = 1.25
= P ( Z >1.25) From Standard Normal Table
= 0.1056                  
c)
To find P(a < = Z < = b) = F(b) - F(a)
P(X < 9) = (9-10)/4
= -1/4 = -0.25
= P ( Z <-0.25) From Standard Normal Table
= 0.40129
P(X < 12) = (12-10)/4
= 2/4 = 0.5
= P ( Z <0.5) From Standard Normal Table
= 0.69146
P(9 < X < 12) = 0.69146-0.40129 = 0.2902