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shikhargmat
- Junior | Next Rank: 30 Posts
- Posts: 18
- Joined: Fri Jun 18, 2010 11:39 am
Although I do not find it difficult while solving the Probability questions, but do have a conceptual doubt.
While solving a Dice problem e.g. 2 dice are there. 1 showing Prime and other showing composite. Find probability.
In these problems we take 2 cases.
1) Prime on Die one and Composite on Die 2.
2) Composite on Die One and Composite on Die 2.
And add the results.
1/3 * 1/2 + 1/2 * 1/3
So in a way we can say that we are taking all the arrangements or combinations.
Whereas for Balls pickup problems such as this:
Find probability of picking 5 balls out of 8white and 4 Red (Condition: we must pick 3 white and 2 Red).
For such questions we solve as:
8C3 * 4C2 / 12C5
i.e. we took the combinations (and not permutations).
While solving, i know how to solve these kind of problems but still I find difficulty at conceptual level. Whether we ned to take all permutations or combinations?
While solving a Dice problem e.g. 2 dice are there. 1 showing Prime and other showing composite. Find probability.
In these problems we take 2 cases.
1) Prime on Die one and Composite on Die 2.
2) Composite on Die One and Composite on Die 2.
And add the results.
1/3 * 1/2 + 1/2 * 1/3
So in a way we can say that we are taking all the arrangements or combinations.
Whereas for Balls pickup problems such as this:
Find probability of picking 5 balls out of 8white and 4 Red (Condition: we must pick 3 white and 2 Red).
For such questions we solve as:
8C3 * 4C2 / 12C5
i.e. we took the combinations (and not permutations).
While solving, i know how to solve these kind of problems but still I find difficulty at conceptual level. Whether we ned to take all permutations or combinations?
