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 #18
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BERTIE (or anyone who really understands)   Please can you help here:      

 Different (but realted ) Question:

 

I have six bottomless jars of lollies.    They are  Red, Green, blue, yellow, orange and black respecitvely.

I want to randomly choose 2 lollies. How many combintions are in the sameple space and what is the probability that one is red and one is green.

 

I am told it is appropriate to use the stars and bars method for a question like this

https://www.youtube.com/watch?v=5hF59P8tmQc

 

so there are (2+6-1)C2 possible combinations.     7C2 = 21

I just want one of those so the probability is   1/21

 

Now I want to toss 2 identical dice.    and I want to know what is the probability of tossing a 2 and a 3

For a question like this it is normal to drawn a 6 by 6 grid.  There are 36 possible outcomes but there are 2 ways that I can get a 2 and a 3.   So the prob of throwing a 2 and a 3 is    2 /36  = 1/18

 

NOW why are these questions done differently.

6 colours all equally likely to be chosen     I chose 2 of them

6 numbers all equally likely to be chosen    I chose (roll) 2 of them.

 

To me the questions seem Identical but I am assued that they are not.

My question is  WHY  ARE  THEY  DIFFERENT ?????

 

Can anyone to try and explain this to me, I just don't get it.     sad

I'd be very grateful if anyone could get the difference through to me.  

Mar 6, 2016
 #2
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Mar 6, 2016

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