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[*]Permutation → Order matters
[*]Combination → Order doesn’t matter

Example:
  • Password Formation: Choosing 3 digits from {1,2,3,4} to form a password
    Permutation (because "123" is different from "321")
  • Selecting a Team: Choosing 3 people from a group of 10
    Combination (because "Alice, Bob, Charlie" is the same as "Charlie, Bob, Alice")
You don't always need to use the permutation formula explicitly; often it's enough to reduce the possibilities step by step and multiply them.
Example:
  • Password Formation: Choosing 3 digits from {1,2,3,4} to form a password
    Permutation (because "123" is different from "321") 4P3 = 4!/(4-3)!
    Reduce possibilities step by step and multiply = 4*3*2

Sangeeth217
Is there any good material to get clarity on when to apply permutation and when to apply combination? I'm getting confused with more questions i look into
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Sangeeth217
Is there any good material to get clarity on when to apply permutation and when to apply combination? I'm getting confused with more questions i look into

Would suggest to go through every sub-topic in this: https://gmatclub.com/forum/combinatoric ... 06266.html
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Can someone explain why 30C1 would be a choice?

My answer was 435.

Is it because of replacement?
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30C2 is for different unique bag options. (such as AB, AC, AD, BC, BD, CD)
30C1 should be added for unique options. (such as AA, BB, CC, DD)
There is no condition in the question that they should not be the same.
Khilji0007
Can someone explain why 30C1 would be a choice?

My answer was 435.

Is it because of replacement?
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There are 30 unique handbags to choose from (3 sizes x 10 colors)

We have to select 2 from these 30.

We are not given in the question that these 2 selections need to be 2 distinct handbags, Sarah can select 2 handbags with same configuration (ex. 2 Large Red handbags)

Therefore, we will use the formula for combinations with repetition: \((n+r-1)C_r\) => \((30+2-1)C_2 = 31C_2 = \frac{(31*30)}{2} = 465\)

Answer C.
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