Finish the chart by putting in the totals in a new
column on the right, and also in a new row on the
bottom. When you add correctly across and down,
you should get the same number in the bottom
right for both totals. In this case 320.
----------------------------------
| Light smoker | Smoker | Totals |
-----------------------------------------
Men | 50 | 200 | 250 |
-----------------------------------------
Women | 60 | 10 | 70 |
-----------------------------------------
Totals | 110 | 210 | 320 |
-----------------------------------------
Find the probability that a person selected is a man
or a light smoker,
I'll color red all the ones that are either a man or a light smoker:
----------------------------------
| Light smoker | Smoker | Totals |
-----------------------------------------
Men | 50 | 200 | 250 |
-----------------------------------------
Women | 60 | 10 | 70 |
-----------------------------------------
Totals | 110 | 210 | 320 |
-----------------------------------------
That's 50+200+60 = 310 out of 320, or 310/320,
which reduces to 31/32.
Find the probability that a person selected is woman or light smoker,
----------------------------------
| Light smoker | Smoker | Totals |
-----------------------------------------
Men | 50 | 200 | 250 |
-----------------------------------------
Women | 10 | 60 | 70 |
-----------------------------------------
Totals | 110 | 210 | 320 |
-----------------------------------------
That's 50+10+60 = 120 out of 320, or 120/320,
which reduces to 3/8.
Find the probability that a person selected is a smoker man,
----------------------------------
| Light smoker | Smoker | Totals |
-----------------------------------------
Men | 50 | 200 | 250 |
-----------------------------------------
Women | 60 | 10 | 70 |
-----------------------------------------
Totals | 110 | 210 | 320 |
-----------------------------------------
That's 200 out of 320, or 200/320,
which reduces to 5/8.
If a man is selected Find the probability that he is a smoker?
This one is different because we are given that a man is selected.
We were not given that in the others. So we eliminate the women
and the total, for the total includes the women.
----------------------------------
| Light smoker | Smoker | Totals |
-----------------------------------------
Men | 50 | 200 | 250 |
-----------------------------------------
Women | 60 | 10 | 70 |
-----------------------------------------
Totals | 110 | 210 | 320 |
-----------------------------------------
So this is just the 200 out of the 250, or 200/250,
which reduces to 4/5.
Edwin
