12 Permutation n Combinations problems

[ketank]

Hi coyote, For 1) as the ques. talks about interview schedules and hence order of candidates should matter. I could'nt think of any other way....

[coyote]

Of course Ketan, the order matters. But two candidates when interviewed "together" in the same slot, then the order should not matter. I am referring to the first slots on each day.

[ketank]

Q9) The ans is B provided we assume that 3 digit, 4 digit and 5 digit numbers can be created.

3 digit numbers = (1)*(4P2) = 12
4 digit numbers = (4P1)*1*(3P2) = 24
5 digit numbers = (4P2)*1*(2P2) = 24

Adding above = 60

[vinuharan]

I was thinking on the same lines but I think we are repeating certain possibilities here. The order of the two candidates in the first slot of any of the 3days does not matter. I think in the 9! part we assume both such possibilities


day 1: A B ; C

(or)

day 1: B A ; C
(where A,B, C are candidates)
If this is true we need to eliminate those repetitive conditions. Don't know how

Let me know if I'm wrong.

since we are finding the possible number of schedules,i think we should treat AB and BA as different.
If we want to remove the repetitions we should go for combination.Even then i dont get E as answer.

[coyote]

They have said the 'candidates will be interviewed "together" ' .I think we should consider them as a pair and not individually.
I,too, don't see how to put this down mathematically.

[ketank]

Q11) Ans is D

1 D and 3 ADs = 3C1*5C3
2 Ds amd 2 ADs = 3C2*5C2

Adding = 60

[ketank]

For Q 12) My ans is coming 1548. However, it's not matching with the supplied options.

Could'nt understand Q10) properly.

[vinuharan]

10)
7*6*5*2*1=420
For the first three positions i considered both police officers and criminals and for the last two position i considered only 2 criminals.
correct me if iam wrong...

[wildorchidz]

Thanks guys for all the explanation .. I was really goin mad with these...

[ketank]

welcome