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?

Question

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.

Answer 1

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

Answer 2

so i am looking at it from the guy Steves response

if 40% are red and then red and blue is 90% wouldn't you break that down to be 40% of the 90 is red so 50% is blue? and then for the probability of having red and orange would be 50%. meaning the amount of orange is 10%? making Red =40% Blue=50% and Orange =10% All Equalling 100% of the marbles in the bag?

Answer 3

Yes, that is correct. We can calculate the probability of blue by subtracting the probability of red from the total probability of red and blue: 90% - 40% = 50%. And since the probability of red and orange is 50%, the probability of orange must be 10%. So Red = 40%, Blue = 50%, and Orange = 10%, which add up to 100%.