00:01
So, let us start with the concept which we are going to use here for this question.
00:06
We have to use z -score formula which will be equal to x -bar minus mu by sigma where x -bar is the sample mean, mu is the population mean, sigma is the standard deviation.
00:15
So, as per the question for the a part, we have to find the probability that a battery lasts more than 4 hours.
00:26
More than 4 hours.
00:28
Now more than 4 hour means to say 4 multiplied by 60 of minutes that will come out equals to 240 minutes.
00:36
So we need to calculate the area under the normal distribution curve to the right of 240 minutes.
00:44
So we just use first the z -scope formula which can be equals to x bar minus mu by sigma.
00:49
That one goes to be, see the x bar value is given 240 minus or mu is given to you.
00:58
260 by sigma is given to us that is 50.
01:01
So this will comes out equals to negative of 0 .4.
01:07
So we have to find the probability using the normal distribution table for the right tailed that is p of x greater than 2 to 40 minutes.
01:17
So that's going to goes to be p z greater than 2 negative to 0 .4.
01:22
So by using normal distribution table you will get this value 0 .6554.
01:29
So the probability for the lasting of 4 hours that means 240 minutes is about 0 .6554.
01:39
So this will be the required answer for first part of this question.
01:43
Now in b part we have to calculate the quartile of the the battery where need to find the values q1 and q2.
01:51
So first of all z is corresponding to the 75 percent means quartile 1 is the value of p where z greater than 2 z1 and that will becomes out to 0 .25 1 minus 0 .75 will become 0 .25.
02:10
So using the standard normal distribution for the first quartile, p value will comes to 0 .6745.
02:20
Now we have to find the quartile values...