00:01
In this problem, let x will be the lifespan of cell phone, and we will assume that variable x has the normal distribution.
00:14
Population mu is 33, and population standard deviation sigma is 5 .5.
00:25
Task a, we should find the probability that x is less than 24.
00:34
This equals probability that z is less than 24 minus population mean 33 divided by standard deviation 5 .5.
00:50
And this will be probability that z is less than minus 1 .63.
00:57
And by using that score table, we can find the corresponding probability 0 .0 .15.
01:11
So this is the answer for the part a.
01:14
The next part b.
01:19
We should find the probability that x will be between 24 and 36.
01:29
This equals probability that x is less.
01:33
Less than 36 minus probability that x is less than 24...