# Probability question

There is a 80% chance that Wednesday's mail will be delivered before noon on Wednesday and a 40% chance that Thursday's mail will be delivered before noon on Thursday. If these probabilities are independent, what is the probability that the mail will arrive before noon at least one of those two days?

## Answers and Replies

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Hurkyl
Staff Emeritus
Gold Member
What thoughts have you had so far?

heh guess I should be posting what ive done on these instead of just posting the question :)

ok well all I know is that its .8 (x) + .4 (x) , but I have no idea what the variable x is. I cant just add .8 and .4 because that would be greater then one. So i guess I just need help figuring out what x is

Hurkyl
Staff Emeritus
Gold Member
Well, why do you think that?

or maybe this has something to do with the independent test...

One way to go about solving "at least one" problems, is to think of the probability that none happen.

so 1-.2(.6)? which is 88% then?

Evilpony,

Does that answer (88%) seem to make sense? Should it be greater than the probability on either individual day?