In manufacturing a particular set of motor shafts, only shaft diameters of between 38.20 and 37.50 mm are usable. If the process mean is found to be 37.80 mm with a standard deviation of 0.20 mm, what percentage of the population of manufactured shafts are usable?

Answer:

we can conclude that  91.04% population of shafts are usable

Explanation:

Given that;

X[tex]_{min}[/tex] = 37.50 mm

X[tex]_{max}[/tex] = 38.20 mm

mean μ = 37.80

standard deviation σ = 0.20 mm

This problem is based on normal probability distribution so, to get the probability, we must calculate; z = x-μ / σ

so;

Z[tex]_{min}[/tex] = (X[tex]_{min}[/tex] - μ) / μ = (37.50 - 37.80) / 0.20 =  -1.5

Z[tex]_{max}[/tex] = (X[tex]_{max}[/tex] - μ) / μ = (38.20 - 37.80) / 0.20 =  2

Hence;

P( 37.50 < X < 38.20 ) = P( -1.5 < Z < 2 )

P( 37.50 < X < 38.20 ) = P( 0 < Z < 1.5 ) + P( 0 < Z < 2 )

from the standard normal table table;

P( 37.50 < X < 38.20 ) = 0.4332 + 0.4772

P( 37.50 < X < 38.20 ) = 0.9104 = 91.40%

Hence, we can conclude that  91.04% population of shafts are usable

What is manufacturing machining ?

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