Question

X is a normally distributed random variable with a mean of 9.00. If the probability that X is less than 10.76 is 0.67 (as shown below), then what is the standard deviation of X

Answer 1

Standardize:
mu=9
X=10.76
P(Z)=P((X-mu)/sigma) = 0.67
From Normal Distribution tables, P(0.44)=0.67
So Z is now known.
Can you find sigma?

Answer 2

Thank you