Please suggest when to use nCr formula to select a item for a group.
lets says we need to select 1 blue ball from 5 blue,4 Green & 3 Yellow Balls. - then we can simple take 5/12
Then What is the need of writing 5C1/12 - however 5C1 also gives 5
In other case
lets says we need to select 2 blue ball from 5 blue,4 Green & 3 Yellow Balls. - then we can simple take 5/12 * 4/11 = 5/33
In that case do we need to write it as 5C2 = 10
What will be denominator in this case-- is it 12
so probability is 5C2/12 = 10/12 = 5/6
Please suggest . I am confused.
Logic of selecting items from a group
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- OptimusPrep
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Nikhil, simply take it this way.
nCr is a selection of n things from a total of r things.
For your problems,
1. Select 1 blue ball from 5 blue,4 Green & 3 Yellow Balls
This means. 1 blue ball out of 5 blue balls
and 1 ball out of total 12 balls.
Hence we write 5C1/12C1
2. Select 2 blue ball from 5 blue,4 Green & 3 Yellow Balls
This means. 2 blue ball out of 5 blue balls
and 2 balls out of total 12 balls.
So, we write 5C2/12C2 and on solving this is the same as what you have written.
What you are doing is:(5/12)*(4/11)
It simply means:
(5C1/12C1)*(4C1/11C1) = (1 blue balls from 5 blue balls and total 12 balls)*(1 blue ball from 4 blue balls and total 11 balls). Because the one ball has already been removed.
Does this help?
nCr is a selection of n things from a total of r things.
For your problems,
1. Select 1 blue ball from 5 blue,4 Green & 3 Yellow Balls
This means. 1 blue ball out of 5 blue balls
and 1 ball out of total 12 balls.
Hence we write 5C1/12C1
2. Select 2 blue ball from 5 blue,4 Green & 3 Yellow Balls
This means. 2 blue ball out of 5 blue balls
and 2 balls out of total 12 balls.
So, we write 5C2/12C2 and on solving this is the same as what you have written.
What you are doing is:(5/12)*(4/11)
It simply means:
(5C1/12C1)*(4C1/11C1) = (1 blue balls from 5 blue balls and total 12 balls)*(1 blue ball from 4 blue balls and total 11 balls). Because the one ball has already been removed.
Does this help?
nikhilgmat31 wrote:Please suggest when to use nCr formula to select a item for a group.
lets says we need to select 1 blue ball from 5 blue,4 Green & 3 Yellow Balls. - then we can simple take 5/12
Then What is the need of writing 5C1/12 - however 5C1 also gives 5
In other case
lets says we need to select 2 blue ball from 5 blue,4 Green & 3 Yellow Balls. - then we can simple take 5/12 * 4/11 = 5/33
In that case do we need to write it as 5C2 = 10
What will be denominator in this case-- is it 12
so probability is 5C2/12 = 10/12 = 5/6
Please suggest . I am confused.
You are messing up combination and probability together. Both these concepts are used together is solving probability questions.
Post questions related to combination and probability ... that would be a good point to start.
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solving question is another part of game. I want to be rich in concepts of counting, probability, combinations & permutations.
I am mixing all these 4.
I am mixing all these 4.
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Awesome explanation Ankur. Thanks so much.OptimusPrep wrote:Nikhil, simply take it this way.
nCr is a selection of n things from a total of r things.
For your problems,
1. Select 1 blue ball from 5 blue,4 Green & 3 Yellow Balls
This means. 1 blue ball out of 5 blue balls
and 1 ball out of total 12 balls.
Hence we write 5C1/12C1
2. Select 2 blue ball from 5 blue,4 Green & 3 Yellow Balls
This means. 2 blue ball out of 5 blue balls
and 2 balls out of total 12 balls.
So, we write 5C2/12C2 and on solving this is the same as what you have written.
What you are doing is:(5/12)*(4/11)
It simply means:
(5C1/12C1)*(4C1/11C1) = (1 blue balls from 5 blue balls and total 12 balls)*(1 blue ball from 4 blue balls and total 11 balls). Because the one ball has already been removed.
Does this help?
Can you please provide some reference to guide to counting(combinations & permutations) & probability
Thanks in Advance.