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Report Thread starter 4 years ago
Probability is what I find the hardest in maths, I've been doing questions, and there's two questions that I can't get the answer to. If anyone could answer the question i'd be grateful if you could include how you answered it

1) A bag contains 3 black beads, 5 red beads and 2 green beads. Gianna takes a bead at random from the bag, records its colour and replaces it. She does this two more times. Work out the probability that of the three beads Gianna takes, exactly two are the same colour

2) A bag contains 6 red disks, 4 blue disks and 5 green disks. A fair dice has 4 faces painted red and the other 2 faces painted blue.
Lisa takes a disk at random from the bag and records its colour. Lisa then throws the dice twice and each time records the colour of the face it lands on.
Work out the probability that of the three colours lisa records, exactly two are the same.

Any help would be appreciated, thanks in advance
Badges: 7
Report 4 years ago
For question 1 at GCSE you'd usually draw a tree diagram, but for this question it'd be really time consuming and annoying so I used an alternative method. I found the probability of each colour happening and not happening. I then worked out how many possibilities gave 2 colours the same and multiplied them together. Then you just add them all up to find the final answer. (Hopefully a lot clearer when you see my working)

For question 2, I started you off with a tree diagram to show you this method works just as well. The probabilities you just input in straight from the question, then again multiply them as you normally would using a tree diagram. I've showed you all the possibilities that'd work, so just calculate the rest and add them all up for the final answer.

Make sure to ask me if you're stuck or you don't understand anything in the question. Good luck with your exam Name:  ImageUploadedByStudent Room1432505865.055902.jpg
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