Hello to everyone...

I'm very new to stats and have worked through my assignments but am not sure I'm on the right track.

The question is: Two events, A and B are equally likely. The chance that either A or B happens on a given trial of an experiemtn is 0.70, while the chance that they both happen on a given trial is only 0.40 What is the probability that event A happens?

I know this is probably pretty basic for you all and I am not looking for help with homework...I'm just really new to stats and am finding some of the concepts pretty difficult.

Thanks alot...
Hi Shannon,

Welcome to the forum.

You can use the equation P(A or B) = P(A)+P(B)-P(A and B), since P(A or B) and P(A and B) are given, and P(A)=P(B), it shouldn't be difficult to solve for P(A). Let me know if you have further questions.
Thanks very much for your reply and please bear with me. Am I correct then, in determining that A would be the result of P(A or B) - P(A and B) or .30?

I had determined that I should use the addition equation - as you noted below - and although I know this is relatively simple for the experienced person, I'm having a bit of a time with it.

Thanks again and I appreciate your help...I'm hoping to be able to continue on my own once I'm able to wrap my brain around this concept.

Just substitute the numbers into the formula:

0.70 = P(A)+P(B)-0.40

0.70 = P(A)+P(A)-0.40 since P(A)=P(B),

and solve for P(A).