# The credit score of a 35 year old applying for a mortgage at Ulysses Mortgage Associates is normally

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The credit score of a 35 year old applying for a mortgage at Ulysses Mortgage Associates is normally distributed with a mean of 600 and a standard deviation of 100.
(a) Find the credit score that defines the upper 5 percent.
(b) Seventy-five percent of the customers will have a credit score higher than what value?
(c) Within what range would the middle 80 percent of credit scores lie?

I know the answer they are below.
I have no idea how 5% becomes 1.645 or 75% becomes -.68 or, etc..
Is there a formula in excel to find out how 5% becomes 1.645, or etc????

a) Upper 5% the Z = 1.645
X = 600 + 1.645 * 100 = 764.5
b) Upper 75% the Z = -.68
X = 600 – 0.68 * 100 = 532
c) Middle 80% the Z = -1.28 and 1.28
X = 600 – 1.28 * 100 = 472
X = 600 + 1.28 * 100 = 728