# Math Help - Addition and Multiplication law of probablility

1. ## Addition and Multiplication law of probablility

I'm having trouble doing an assignment based on a Joint Probability Table and was wondering if I could get some help.

This has to do with blood types in the general population

Data Given :

------l A-------lB--------lAB------lO
Rh+ --l34%-----l9%------l4%-----l38%
Rh- --l-6%-----l2%------l1%------l6%

With the data above, i'm supposed to construct a Joint Probability Table and then answer some questions about it. I constructed a JPT and it looks just like the table above except in decimal form with totals of each colums and row. Was wondering if you guys could help me along. Thanks

1. What is the probability that a person will have Type O blood?

0.44

2. What is the probability that a person will be Rh-?

0.15

3. What is the probability that a married couple will both be Rh-?

4. What is the probability that a married couple will both have Type AB blood?

5. What is the probability that a person will be Rh- given that she or he has Type O blood?

6. What is the probability that a person will have Type B blood given she or he is Rh-?

The first two I think i've answer correctly. Any help on the others? Thanks in advance guys

2. The first two are correct,
(3) The pr of both being RH- is equal to the pr of the man having RH- times the pr of the women. So $0.15 \cdot 0.15 = 0.0225$
You can check this answer by the fact that;
Pr. of both being RH+ is $0.85 \cdot 0.85 = 0.7225$ and one of each being $2 \cdot 0.85 \cdot 0.15=.255$ which sums to 1.

(4) The answer is similiar as (3) except the conditional pr of being AB is 0.05.

(5) $\Pr(\mbox{RH-} | O)=\frac{\Pr(\mbox{RH-},O)}{\Pr(O)}=\frac{0.06}{0.44}=0.1364$

(6) Use the same method to calculate this as was used in (5)