Question

Suppose that the lifetimes of TV tubes are normally distributed with a standard deviation of 1.2 years. Suppose also that exactly 20% of the tubes die before 4.5 years. Find the mean lifetime of TV tubes. Carry your intermediate computations to at least four decimal places. Round your answer to at least one decimal place.

_____yrs.

Answer 1

Solution :

X : the lifetimes of TV tubes

σ = standard deviation =1.2 years

Suppose also that exactly 20% of the tubes die before 4.5 years.

That is P(x < 4.5) = 0.20

Using Normal Table ,

z = -0.84

Hence

µ = x - zσ = 4.5 - (-0.84*1.2) = 5.5080 = 5.5

Answer : 5.5 yrs

Find the mean lifetime of TV tubes. Carry your intermediate computations to at least four decimal places. Round your answer to at least one decimal place.

_____yrs.