Answer:
The data is:
From the adults in town:
8% have liver problems, of those:
25% heavy drinkers
35% social drinkers
40% non-drinkers.
92% do not have liver problems (100% - 8% = 92%)
5% heavy drinkers
65% social drinkers.
30% non-drinkers
a) An adult is chosen at random, then:
Has a liver problems
We know that 8% of the adults have liver problems, so the probability is 8%, or 8%/100% = 0.08.
Is a heavy drinker
Out of the 8%, 25% are heavy drinkers, and out of the other 92%, 5% are heavy drinkers, so the total percentage of heavy drinkers is:
(i will use decimal math, because you always should work with decimals instead of percentages)
P = 0.08*0.25 + 0.92*0.05 = 0.066
or 6.6% in percentage form
If a person is found to be a heavy drinker, what is the probability that this person
the proability that some one is a heavy drinker was already found, it is p = 0.066.
Now, of those 0.066 we have:
p1 = 0.08*0.25 = 0.02 have liver problems.
So the probability that, given that some one is a heavy drinker, that her/him also have liver problems is:
P = 0.02/0.066 = 0.3 or 30%.
If a person is found to have liver problems, what is the probability that this person is a heavy drinker?
]We already know that out of the 8% with liver problems, a 25% are heavy drinkers, so here the answer is 25% or 0.25.
If a person is found to be a non –drinker, what is the probability that this person has liver problems.
From the 8% with liver problems, we have 40% of non-drinkers,
So the total proportion of non-drinkers with liver problems is:
p1 = 0.8*0.40 = 0.032
From the 92% with no liver problems, we have that 30% of them are non-drinkers, so here we have:
p2 = 0.92*0.30 = 0.276
The total proportion of non drinkers is:
p1 + p2 = 0.032 + 0.276 = 0.308.
Then if we know that some one is non drinker, the proability that the person has liver problems is equal to the quotient between the proportion of non-drinkers with liver problems ( 0.032) and the total proportion of non-drinkers.
p = 0.032/0.308 = 0.104
or 10.4% in percentage form.