math
posted by Preston .
A bag contains red, blue, and orange marbles. If the probability of randomly selecting a red marble is 0.4 and the probability of selecting a red or blue marble is 0.9 what is the probability of selecting a red or orange marble?
In my opinion, the easiest way to solve these kinds of problems is to assume that you have 100 marbles in a bag.
If 40% are red, then 40 marbles are red.
If 90% are red or blue, then 90 marbles are red or blue.
And so forth.
that doesnt make any sense to me
Just assume that you have 100 marbles. It makes the question much easier to solve rather than assuming that you have some random number x of marbles.

4 red,4 white,4 blue
at random take out 2 , say 1 red 1 white do not replace.
what is probarbility of now picking a)blue
b)red c)white