a bag contains 7 red marbles,1 blue and 1 green. you take one marble from the bag and do not replace it. find the probability of choosing a marble that is blue or green.

do i do 1/10+1/9??

No. If you want to find the probability that the marble you drew is blue or green, then that is just the 2/9, since 2 of the 9 marbles are either blue or green.

If you mean that after the 1st marble was drawn and not replaced, what is the chance of then drawing a blue or green, then that is

If we call P(blue|green) = P(bg), then
P(red,bg)+P(bg,bg)
= 7/9 * 2/8 + 2/9 * 1/8 = 2/9

Huh. I'd not expected the two results to be the same...