Posted by **Alia** on Friday, January 4, 2013 at 6:57pm.

If X is a normal random variable with mean 11, and if the probability that X is less than 12.10 is .72 , then what is the standard deviation of X?

Select one:

a. 3.00

b. 6.25

c. 2.50

d. 1.25

Please note that the answer for the above is stated as c.2.50. However, my answer comes to 1.89 which is not given as an option and I can't figure out where I'm going wrong so please can anyone help me with this problem.

Thanks.

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