The local authorities in a certain city install 10,000 electric lamps in the streets of the city. If these lamps have an average life of 1000 burning hours with a standard deviation of 200 hours, assuming normal distribution, what number of lights might expected

Step-by-step explanation:

It is given:

,

Let x be the random variable that denotes the number of hours the lamp lights up.

what number of lights might expected to fail in the first 800 burning hours

We are required to find the expected number of lights to fail in the first 800 burning hours.

First, we have to find the probability as:

P(Z < 800)

Using the z-score formula, we have:

Using the z-score formula, we have:

=P(z<-1)

Now using the standard normal table, we have:

P(x<800)=P(z<-1)=0.1587

Therefore, the expected number of lights to fail in the first 800 burning hours is:

After how many burning hours 10% of the lamps would be still burning?

We first need to find the z-value corresponding to area = 1- 0.10 = 0.90. Using the standard normal table, we have:

z(0.90)=1.28

Now using the z-score formula, we have:

x= 1000+256

77

step-by-step explanation: