SOLUTION: Find the mean and standard deviation given that 95% of the balls with string have lengths exceeding 490 meters and 99% have lengths exceeding 485 meters. Thanks so much!

Question 648221: Find the mean and standard deviation given that 95% of the balls with string have lengths exceeding 490 meters and 99% have lengths exceeding 485 meters.
Thanks so much!
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Find the mean and standard deviation given that 95% of the balls with string have lengths exceeding 490 meters and 99% have lengths exceeding 485 meters.
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Draw a normal curve.
Mark a point where 95% of the population is to the right.
label that point 490
Note that the z-value of that point is -1.645
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Mark a point where 99% of the population is to the right.
Label that point 485.
Note that the z-value of that point is -2.326
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Create two equations based on x = zs + u
490 = -1.645s + u
485 = -2.326s + u
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Subtract and solve for "s"
5 = 0.681s
s = 7.342
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Solve for "u";
u = 490+1.645*7.342 = 502.08
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Cheers,
Stan H.
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