



 
Paula, If X is a normal random variable with mean μ and variance σ and Z is the standard normal random variable then Z = (X  μ)/σ. You know that μ = 10,000 and when X = 10,625 then Z = 2.5. Substitute into the expression above and solve for the standard deviation σ. Now that you know σ you can convert X = 9,900 to its Zvalue. Penny  


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