# Lifespan

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?

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 answer:

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