Maths probability

You can see my working and the answer i got from that multiplication was wrong! The answer is 13/18 but I don't know how to get that answer- help

Reply 1

Notnek

Original post by Lucofthewoods

You can see my working and the answer i got from that multiplication was wrong! The answer is 13/18 but I don't know how to get that answer- help

You haven't labelled your diagram so it's hard to know what your numbers mean.

E.g. what are 3/8 and 4/8 at the top?

There should be three branches coming from 4/9 at the top since there are three colours.

Reply 2

undercxver

You need three branches are you have three different colours: red, orange and green. If you draw this tree diagram out properly and label it, it will assist you in finding the answer.

I think you need to look at the last bit you've written, it should have been 3/9 x 2/8 rather than 3/9 x 3/8.

Reply 3

Lucofthewoods

Original post by undercxver

but surely if it was 2/8 that's saying the colours were the same not different

Reply 4

undercxver

Original post by ben2000

As @undercxver mentioned, you seem to have gone wrong with the amount of second branches you have. Here's a video showing how to do tree diagrams: https://www.youtube.com/watch?v=HpxsEn_G9EA

To further help you understand where you went wrong, I've answered the question myself and attached images of that to this reply.

Very helpful of you, however it is against the community guidelines to give the full answer OP. Instead you should try assisting them towards the answer.

Reply 5

ben2000

As @undercxver mentioned, you seem to have gone wrong with the amount of second branches you have. Here's a video showing how to do tree diagrams: https://www.youtube.com/watch?v=HpxsEn_G9EA

Here's an image to show how your branches should be:
https://s-media-cache-ak0.pinimg.com/236x/8d/69/33/8d6933b58a7336af0f5d7ef7e0826e4d.jpg

Reply 6

Matureb

Work out the probability that the sweets are the same colour. Then it is easy to see the prob(not same).

Reply 7

In One Ear

Original post by Lucofthewoods

but surely if it was 2/8 that's saying the colours were the same not different

Think about it this way-

The probability the sweets is different is basically going to be 1-(probability they are the same), agreed? Because the sweets are either the same, or different.

So first we need to work out the probability that the sweets eaten are the same (much easier to deal with mentally).

Lets start with the orange sweets, I'm sure you'd agree there are 4 orange sweets (the question says so) and 9 total sweets, so the probability of the first one being orange is 4/9 right?

However now we ate one of the sweets, we have only 8 total, as you correctly deduced in your workings. However we also ate one of the orange sweets, so there are only 3 left that we might randomly pick. So on second dibs, we have only a 3/8 chance of picking orange again...understand? Therefore the chance of picking double orange is 4/9 * 3/8.

Now apply this process to the other two colors and then combine to find the total probability the sweets are the same, in which case the answer to how likely they are to be different should be obvious! :smile: