Question

and Brill deviation of 55 hours. Find the probebility that the mean life of a random sample of 25 such buibs will be

Answer 1

Here X follows normal distribution with mean 750 and sd 55.

So, if we take a sample of size 25,

then $\bar{X}$ follows normal distribution with mean 750 and sd 55/ $\sqrt{25}$ = 11.

a. P[ $\bar{X}$ > 735] = 0.9137

b. P[735? < $\bar{X}$ < 740] = 0.0953

c. P[725 < $\bar{X}$ < 775] = 0.9770

d.P[ $\bar{X}$ < 735] = 0.0863