A survey of the adults in a town shows that 8% have liver problems. Of these, it is also found that 25% are heavy drinkers, 35% are social drinkers and 40% are non-drinkers. Of

those that did not suffer from liver problems, 5% are heavy drinkers, 65% are social

drinkers and 30% do not drink at all. An adult is chosen at random, what is the probability

that this person

i. Has a liver problems? (3 Marks)

ii. Is a heavy drinker (2 Marks)

iii. If a person is found to be a heavy drinker, what is the probability that this person

has liver problem? (2 Marks)

iv. If a person is found to have liver problems, what is the probability that this person

is a heavy drinker? (2 Marks)

v. If a person is found to be a non –drinker, what is the probability that this person has

liver problems. (2 Marks)

(b) The director of admiss

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.

i wish i could u

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i wish i could u

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