Question

if the weather report is for 25% chance of rain on monday and 10% on tuesday whats the chance it wont rain on either days? please explain :)

Answer 1

If you're having trouble thinking about this algebraically, you can draw a 'tree diagram' like the one I've attached.

You list the possibilities that may occur after the conclusion of each event. Here, the first two branches are for Monday. You can have rain (R) or no rain (R with a 'bar' over it). If you have a probability of rain on Monday sitting at 25%, then you must have a chance of 75% no rain on Monday (in red).

Now, after Monday, either it did rain or it didn't. So we now consider what will happen for Tuesday. It will either rain with probability 0.10 or not rain with probability 0.9. We must consider the possibilities at the conclusion of each even preceding it (like I've shown).

The probability of no rain on both days is then

P(R_1 bar) x P(R_2 bar) = 0.75 x 0.90 = 0.675 = 67.5%

Answer 2

wow; thanks so much! (;

Answer 3

You're welcome :)