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Gcse maths exam tomorrow - help!

Ok, I really really need help on this question, because I always do not know how to complete these:

Nicholas has 30 beads in a bag.
9 are white.
8 are green.
13 are blue.

Nicholas takes two beads from the bag at random.
What is the probability that the two beads will NOT be the same colour??

I'm completely clueless on this one, can someone please show me the working out step by step and explain why each step happens?

Thankyou =)
(edited 13 years ago)
Reply 1
Avatar for Serano
Serano
11
Original post by Instincts_2012
Ok, I really really need help on this question, because I always do not know how to complete these:

Nicholas has 30 beads in a bag.
9 are white.
8 are green.
13 are blue.

Nicholas takes two beads from the bag at random.
What is the probability that the two beads will NOT be the same colour??

I'm completely clueless on this one, can someone please show me the working out step by step and explain why each step happens?


It's hard to describe, your best bet is to draw a tree diagram with the probabilities on them, work out all branches combinations which have different colours on them, then add them together
Original post by Serano
It's hard to describe, your best bet is to draw a tree diagram with the probabilities on them, work out all branches combinations which have different colours on them, then add them together


Wouldn't the total amount of combinations be well over 400? :s-smilie:
Reply 3
Avatar for Serano
Serano
11
Original post by Instincts_2012
Wouldn't the total amount of combinations be well over 400? :s-smilie:


No there's 3 principal branches then 3 sub branches on each principle branch

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