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The probability of a randomly selected hard drive from the company lasting between 2 years 3 months and 3 years 3 months is 32.22%
Given here,
Mean (μ) = 3 years 6 months
= (3×12)+6 = 42 months
Standard deviation (σ) = 9 months
We will find the z-score using the formula: z = (X - μ)/σ
Here X₁ = 2 years 3 months
= (2×12)+3 = 27 months
and X₂ = 3 years 3 months
= (3×12)+3 = 39 months
So, z (X₁ =27) =
and z (X₂ =39) =
According to the standard normal table,
P(z> -1.666...) = 0.0485 and P(z< -0.333...) = 0.3707
So, P(27 < X < 39)
= 0.3707 - 0.0485
= 0.3222
= 32.22 % [Multiplying by 100 for getting percentage]
So, the probability of a randomly selected hard drive from the company lasting between 2 years 3 months and 3 years 3 months is 32.22%