Mean

#1
The lifetimes of interactive computer chips produced by a certain manufacturer are normally distrubuted with aprameters u = 1.4 x 10^6 hours and ro = 3 x 10^5 hours. Wha tis the approximate probability that a bach of 100 chips will contain at least 20 whose lifetimes are less than 1.8 x 10^6 hours?

In order to complete this problem don't I have to find the mean first? Then I can find the z value, use z table and then find probability? Is this the correct process?
 

JohnM

TS Contributor
#2
In the first half of the problem, use the given mean and s.d. and the normal distribution tables to determine the proportion of chips in the population with lifetimes less than 1.8 x 10^6 hours.

Then, once you determine this probability, use the normal approximation to the binomial to compute the probability that at least 20 of a batch of 100 are below this time.