The lifetime of a light bulb is a random variable with a normal distribution of x = 300 hours, σ = 35 hours.
a) What is the probability that a randomly selected light bulb will have a lifespan of more than 320 hours?
b) Up to what value of L hours can the lamp life be expected to last longer than L hours with a probability of 0.25?

Correct result:

p =  0.2839
L =  323.6 h


μ=300 h σ=35 h  xN(μ,σ) t>320 h  p=0.2839
L=323.6=16185=16185 h=323.6 h

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