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S1 probability question?? please help

5)
There are 15 beads in a bag; seven beads are red, three are blue and five are green. Three beads are selected at random from the bag and not replaced. Find the probability that
a) the first and second beads chosen are red and the third bead is blue or green
b) one red one blue and one green bead are chosen

what do I need to do to do this as when I try drawing a tree diagram it doesn't work and without one I'm stuck what to do? please help :smile:
Reply 1
Ah I guess it is quite complicated with a tree diagram. Have you tried just writing them down? That's what I would do.
So for probability of red : 1st time = 7/15. 2nd time = 6/14. 3rd time = 5/13.
You could do it like that and just multiply/add whatever you need. Personally that's how I would do it because I struggle with tree diagrams when it comes to more than two things.
Original post by majmuh24
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Please see the forum rules, and don't post fully worked solutions straight off, particularly when they're not correct.

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