00:01
It's given in this exercise that daily household television viewing time, we'll call that random variable x, is normally distributed with the mean of 8 .35 hours and standard deviation of 2 .5 hours.
00:15
For part a, we are asked for the probability that a household views television between 3 and 11 hours a day.
00:24
So this is the probability that x is between 3 and 11.
00:30
And this can be re -expressed as the probability that x is at most 11 minus the probability that x is less than 3.
00:42
And now let's use software to solve this.
00:47
So the first term is the probability that x is at most 11.
00:50
So if we go to excel, for example, type equals to start computation.
00:55
We want to use the normal distribution function, so we select that, and we enter 11 for the first argument, and then the mean and standard deviation of our distribution.
01:08
And for the cumulative argument we enter true because we want the probability that x is anything up to 11, and hit enter and we get .8554.
01:24
And then we do the same thing for x equals 3.
01:27
So we can actually recycle the formula we've already entered, except change the first argument to 3, and we get .01 .62.
01:44
And we get rounded to four decimal places .833.
01:55
For part b, we were asked how many hours of television viewing must a household have in order to be in the top 2 % of all households.
02:06
So mathematically what this means is there is some amount of television viewing in the household, that's x, such that the probability of viewing at least that much is only 2%, or 0 .02.
02:25
Here we can use the normal inverse function in excel, which is a number...