00:01
Okay, we are told that 25 % of the population smoke, which means p of smoking is 0 .25, which implies p of not smoking is 1 minus that.
00:23
So 0 .75.
00:26
So here is a binomial problem.
00:30
We have success and failure.
00:32
Success here is smoking .25 and failure.
00:35
Not smoking, 0 .75.
00:39
And the first one we're doing here is all 23 are not smokers.
00:47
So that means then.
00:48
0 .75 is not smoking, power 23.
00:53
I need all 23, not smoking.
00:56
That i can work out on a calculator.
00:58
0 .00133.
01:04
We want here four places.
01:07
So 0 .013 is the answer.
01:11
Now part b, exactly 6 smoke.
01:15
So 0 .25, power 6.
01:18
6 smoking.
01:19
0 .75, power 17, 23 minus 6.
01:26
And that can be done 236.
01:31
Different ways.
01:35
The binomial number and that will be 23 c6 which you can work out on a calculator the ti 84 plus press the math button go across to prob the arrow key down to item 3 ncr just type it in so 100 947 so this i can work out now on a calculator and what i would get is 0 .185257 so 18583 to 4 decimal places.
02:24
Now that we can do a bit quicker with the calculator with a function called binom pdf.
02:32
So t -984 plus binom pdf.
02:38
And what i do to get that, i press second followed by vars, vars, on the right just below the arrow keys.
02:48
That brings up the menu for distributions.
02:52
And you can't see it yet.
02:53
With the arrow key, go down past number nine to you reach item a, binon pdf.
03:00
Press enter.
03:02
Trials will be 23, the number of adults you're choosing here.
03:07
P value is 0 .25.
03:08
And the x value is six smoke.
03:18
If i do that and paste it, i'd have got the same answer, 0 .1853.
03:30
This answer is there.
03:35
Now, part c, exactly four smoke.
03:39
Again, do it two ways.
03:42
It could be 0 .25, power of 4, 0 .75, power of 19.
03:50
And then 23, 4.
03:53
That's for the binomial formula.
03:57
4, easier, binom, pdf, 23 .25, 4.
04:12
And that will be, back to the calculator...