Question

Suppose two makes of electric bulbs A and B are tested and observed. Bulbs of make A exhibit mean life of 900 hrs. and standard deviation of 30 hrs. Those of make B show mean life of 860 hrs. and standard deviation of 20 hrs. Find the probability that the mean life based on a random sample of 40 bulbs of make A being, say, 28 hours less than the mean life of bulbs of make B based on a random sample of 30 bulbs.

Answer 1

Answer:

0%

Step-by-step explanation:

Since n in both cases are greater or equal to 30, we will assume a normal distribution.

A: μ₁=p=900 hours  σ/sqrt(n) =30/sqrt(30) =4.75

So, since the distribution is normal, 99 % is between (900-3(4.75) ,900+3(4.75)) or (885.75, 914,75).

B; μ=p=860 hours  20/sqrt(40)=3.65

Again, since the distribution is normal 99 % is between (860-3(3.65),860+3(3.65)) or  (849, 871).

They do not intersect, let alone mean life of bulbs of make A is less than those of make B.