Homework help

#1
Hello. I have a minor set back on my homework. So I have a homework problem which states

find the probability of the indicated event if P(E)=0.25 and P(F)=0.45. My first question is Find P(E or F) if P(E and F)=0.15.

I am not sure which rule to use. I was thinking that the The General Addition Rule was the right one, but I am very unsure.


I just need a better understanding of this problem because my Prof is no help.


Thank You. :)
 

Martingale

TS Contributor
#3
Hello. I have a minor set back on my homework. So I have a homework problem which states

find the probability of the indicated event if P(E)=0.25 and P(F)=0.45. My first question is Find P(E or F) if P(E and F)=0.15.

I am not sure which rule to use. I was thinking that the The General Addition Rule was the right one, but I am very unsure.


I just need a better understanding of this problem because my Prof is no help.


Thank You. :)
P(E or F)=P(E)+P(F)-P(E and F)
 
#4
I don't think that P(E or F) is just adding them together. There will be some overlap in occurances: both = (P(E) * P(F)) = .1125 unless your problem specifically states that E and F are exclusive. To get P(E or F), then, add their probabilities together and subtract P(E and F).
.25 + .45 - .1125 = .5875

This answer can be confirmed by finding 1 - P(!E and !F).
neither = (1-P(E) * 1-P(F)) = .4125
1 - .4125 = .5875