Question

How do you find the area between two values under the normal curve?

Answer 1

Solution:
Lets assume X is normal random variable with
Mean () = 100
Standard deviation() = 15
Now assume we need to calculate probability or area between 70 and 130, First we will convert this raw scores in Z score which can be calculated as
i.e. P(70<X<130) = P(X<130) - P(X<70)
Z-score can be calculated as
Z-score = (X-)/
Z = (70-100)/15 = -2
Z= (130-100)/15 = 2
From Z table we found a p-value
P(70<X<130) = P(Z<130) - P(Z<70) = 0.97725 - 0.02275 = 0.9545
So there is 95.45% area under the 70 and 130.