00:01
Okay, we are told that on average 75 people enter a store per hour.
00:08
It's a put -on type question.
00:10
And the first step is find the average for four minutes.
00:14
All you do is we have 75 and four minutes is equal to four over 60th of an hour.
00:31
So it's one 15th of an hour.
00:35
So just divide this by 15 and get the average for that.
00:39
So 75 divided by 15 is simply 5.
00:44
So on average, every four minutes, five people should come in.
00:49
That's my new value, the mean.
00:55
Now, to work out a chance of nobody coming in in four minutes, we use the function called poisson pdf on the t.
01:06
Ci 84 class calculator.
01:09
And to find that function, what you do, you press second followed by vars, on the right just below the arrow keys.
01:19
That brings up the menu for distributions.
01:22
To find poisson, with the arrow key, go down past item 9.
01:26
Keep going down until you reach item d, quasson pdf, and press enter.
01:32
And the input is the mean, which here is 5, and the x value here is 0.
01:40
So plus on pdf, 5.
01:44
And if i do that, and paste that, i get the answer 0 .00 -673737 and so on.
01:55
And what i want here, okay, no mention of accuracy.
02:02
So we'll say then, 0 .00677.
02:06
Four to five decimal places.
02:11
And that's the answer for the first one.
02:16
Next one is more than three people enter the store...