# CAT questions: Permutations & Combinations - Videos

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https://www.dropbox.com/s/mw6bgkr5mo1sgy1/CAT%20questions-%20P%26C.pdf?dl=0

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1. Sharath Chandra

Sir…the Dropbox file is giving invalid format wat to do for that??

2. Joseph Suganthan

Sir,

From 3 red balls, 4 green balls and 2 white balls, how many selections
can be done such that atleast one of each kind is selected?

Is the answer 3*4*2 or 7*15*3?

Thank you.

3. Meghana Mittal

Sir, In qn no. 2,
What if 5 is not there in the 3 digit no. Then shouldn't it be 5+ 8*9*5 = 365 ways in total

4. Madhurmeet Singh

Greetings sir,
I've tried to come to a formula for questions like Q4.
The sum of all the number of a N digit number will be
(Sum of digits)x(N-1)!x(111..n times)
i might have read it somewhere but it just struck me right now while solving, let me know if there is any alterations required in this.
Though this works only when the digits are non repeating and there is no 0 in the digits given.

5. Pavan Kumar Reddy V

Hello sir, these previous questions workshops are very helpful at this time. Please do previous questions workshops for all the topics and upload in YouTube. Please sir. Thank you

6. shubham sharma

Sir ,what will be the answer to the 13 th question. Could you please explain.

7. Sir in question 3 why aren't we multiplying the answer by 4? Because there are 4 cities and every city has 12 ways to go and return to it without using the same path?

8. neeraj pandey

sir are these actual cat ques?

9. neeraj pandey

for question 10 we can do:- 21c3 – 10c3 – 11c3

21c3 :- Meaning forming triangles from 21 points of which no 3 points are co-linear.

(10c3) : Meaning subtracting those triangle which could have been formed from 10 points of which no 3 are co-linear but here these triangles could not be formed as all 10 points are co-linear

(11c3): Meaning subtracting those triangle which could have been formed from 11 points of which no 3 are co-linear but here these triangles could not be formed as all 11 points are co-linear