# Homework help

#### LeslieF

##### New Member
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.

#### th3plan

##### New Member
P(E OR F) its like adding so .25+.45
P(E AND F) is multipling rule so .25*.45

Thats it

#### Martingale

##### TS Contributor
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)

#### WhiteCog

##### New Member
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

#### LeslieF

##### New Member
Thank you all so much. I understand now. I feel like a dummy lol.