Bulb life

Tests show that the lives of light bulbs are normally distributed with a mean of 750 hours and a standard deviation of 75 hours. Find the probability that a randomly selected light bulb will last between 675 and 900 hours.

Correct answer:

p =  0.818

Step-by-step explanation:

m=750 h σ=75 h  p=N(675<X<900,m,σ)  m2=m2 σ=7502 75=600 m4=m+2 σ=750+2 75=900  1σ2σ3σ rule  p=2 0.341+0.136=0.818

Use the normal distribution table.

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