# 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?

Correct result:

p =  0.284
L =  323.6 h

#### Solution:

$μ=300 \ \text{h} \ \\ σ=35 \ \text{h} \ \\ \ \\ x ... N(μ,σ) \ \\ t > 320 \ h \ \\ \ \\ p=0.2839=0.284$
$L=323.6=\dfrac{ 1618 }{ 5 }=323.6 \ \text{h}$ Our examples were largely sent or created by pupils and students themselves. Therefore, we would be pleased if you could send us any errors you found, spelling mistakes, or rephasing the example. Thank you!

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