Question

The guaranteed average life of a certain type of electric light bulbs is 1000 hours with a standard deviation of 125 hours

Answer 1

Answer:

Explanation:

The question is incomplete so i mentioned the other question like the question you have given. Hope It will  help you.

The life time of a certain brand of an electric bulb may be considered as a random variable with mean   1200 hours and standard deviation 250 hours. Find the probability using central limit theorem has the average  life time of 60 bulbs exceed 1250 hours.

Solution:

Given that n=60

mean = 1200, S.D = 250

Let  x₁ be the life time of an electric bulb.

   

X = x₁ + x₂ + ..x₆₀ / 60

By central limit theorem

ₓ⁻ ≈ N(μ,σ²/n)

= p(Z > 1.55)

= 0.5 - 0.4394

p(x > 1250) = 0.0606