A new extended-life light bulb has an average life of 750 hours, with a standard deviation...

A new extended-life light bulb has an average life of 750 hours, with a standard deviation of 50 hours. If the life of these light bulbs approximates a normal distribution, about what percent of the distribution will be between 650 hours and 850 hours?

Expert Solution

µ =    750
σ =    50
we need to calculate probability for ,
650   ≤ X ≤    850
X1 =    650   ,   X2 =   850

Z1 =   (X1 - µ ) / σ = (   650   -   750   ) /    50   =   -2.0000
Z2 =   (X2 - µ ) / σ = (   850   -   750   ) /    50   =   2.0000

P (   650   < X <    850   ) =    P (    -2   < Z <    2.000   )

= P ( Z <    2.000   ) - P ( Z <   -2.000   ) =    0.97725   -    0.022750   =    0.9545(answer)
excel formula for probability from z score is =NORMSDIST(Z)

orchestra answered 2 years ago

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