Double counting…if you select say A and B as the 2 women in your 8C2 and then in the 13C2 you add C and D. In another case you select C and B in the 8C2 and A and D in the 13C2. Yet another you select A and C in the 8C2 and B and D in 13C2. You are treating all as different cases. But they are one and the same.
The term “Double counting” in PnC doesn’t necessarily mean exactly double. It could be 3-4 times; we use “double counting” to indicate that some multiple counting type error is present.
In the example I took with AB and CD, we could also get AC and BD, AD and BC and so on; each case would be counted 6 times. (With 3 women each case would be counted thrice I think.)
Yes we certainly could 🙂 I took the approach with many cases to show how it can save time in calculation there.
As for writing…well, depends on the centre I suspect. I tried writing a few things once (around 2015 I think it was) just out of curiosity and the invigilator had no issues with it but a year or two later my friend who tried the same was told “don’t write anything except your reg no” till the test starts.
CAT-holics 
Hi, What is wrong with this approach?
Step 1 : Select 2 women = 8C2
Step 2 : Select 4 from the remaining = 13C2
Answer=8C2*13C2
please help
Double counting…if you select say A and B as the 2 women in your 8C2 and then in the 13C2 you add C and D. In another case you select C and B in the 8C2 and A and D in the 13C2. Yet another you select A and C in the 8C2 and B and D in 13C2. You are treating all as different cases. But they are one and the same.
regards
J
Sir (8c2*13c4)/2 wats wrong in this soln?
The term “Double counting” in PnC doesn’t necessarily mean exactly double. It could be 3-4 times; we use “double counting” to indicate that some multiple counting type error is present.
In the example I took with AB and CD, we could also get AC and BD, AD and BC and so on; each case would be counted 6 times. (With 3 women each case would be counted thrice I think.)
regards
J
Hi!
I played around with the Pascal Triangle values and I must say, it is pretty versatile and handy!
Also, here can’t we subtract the two cases where only 1 or 0 women selected and subtract it from total. Answer seems to come the same.
Another thing, before starting the CAT paper, are we allowed to write on the rough pad? Stuff like say, pascal triangle, cubes, etc.
Yes we certainly could 🙂 I took the approach with many cases to show how it can save time in calculation there.
As for writing…well, depends on the centre I suspect. I tried writing a few things once (around 2015 I think it was) just out of curiosity and the invigilator had no issues with it but a year or two later my friend who tried the same was told “don’t write anything except your reg no” till the test starts.
regards
J