SOLUTION: the lengths of steel rods cut by a machine are normally distributed with mean 13.8com. It is found that 1.5% of all rods are less than 13.2cm long. Find the standard deviation of r

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Question 691603: the lengths of steel rods cut by a machine are normally distributed with mean 13.8com. It is found that 1.5% of all rods are less than 13.2cm long. Find the standard deviation of rod lengths produced by this machine.
Answer by stanbon(75887) About Me  (Show Source):
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the lengths of steel rods cut by a machine are normally distributed with mean 13.8com. It is found that 1.5% of all rods are less than 13.2cm long. Find the standard deviation of rod lengths produced by this machine.
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Draw a normal curve.
Put x = 13.8 in the middle
Plot x = 13.2 on the horizontal axis
Shade the tail to the left of 13.2 ; That tail has area 0.015
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Find the z-value with a left tail of 0.015:
invNorm(0.015) = -2.1700
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Find the standard deviation using x = z*s + u
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13.2 = -2.17s + 13.8
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-2.17s = -0.6
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s = 0.2765
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Cheers,
Stan H.
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