the ticket window question was amazing but sir shouldn’t it be mentioned that the window does not have any change of itself … coz the question can be interpreted as probability of the 10th person being the first to have 2 re coin..
suppose it was asked the probability that of 3rd person to wit… how would we approach this problem????
Girish, yes 3.8xx is what it comes I think, don’t remember exactly. And true, the ticket window should not have any change to begin with. For the third guy to be the first to wait, the first guy has to have a 1 rupee (since if the first guy has a 2 rupee, he will be the first to wait), and the second has to have a 2 rupee (since if the first and second both have 1 rupee, the third guy will not have to wait. The third guy will now need to have a 2 rupee. So we can calculate the probability accordingly. For the 5th guy it is a lot more complicated though…
Ratish, thanks for the kind words. I am glad it is proving to be of help.
I believe that these methods are also the most useful in the actual exam – not for the majority of questions, but if you can do even a couple of questions without writing, it gives a tremendous morale boost. And anyone can learn how to do this really, all it takes is the right mindset (instead of the write mindset 😉 )…and a lot of practice! The bonus is that trying this in practice also forces you to strengthen your basic concepts….
Exactly.
I spend 2 hours daily travelling (back and forth) and hence I always try to solve the questions on your website and other CAT related websites mentally. And it really helps!
I believe the best preparation for CAT is not by learning formulae or studying numerous hours a day, but by making your brain actually think and to keep it ticking everyday. 🙂
Vaibhav, in that case it would be a truly nasty problem, with horrendous calculations – but one that would never be asked in a CAT. The thing is, if you see something with such calculations, you should recognise that there must be a trick.
Remember that in an exam like the CAT, they are trying to differentiate good candidates from bad. A question which everybody could answer would be useless to them – but so would one which nobody could answer!
Hie,
In the ticket window question, all the arrangements of children are equally likely. So we can have a situation in which each of the 9 children ahead of the 10th child has Re 1 with them and the 10th child is the first one to have Rs 2. In that situation won’t the 10th child be the first one to wait? What am i missing?
CAT-holics 
Thank you J 🙂
the ticket window question was amazing but sir shouldn’t it be mentioned that the window does not have any change of itself … coz the question can be interpreted as probability of the 10th person being the first to have 2 re coin..
suppose it was asked the probability that of 3rd person to wit… how would we approach this problem????
for the last one… i got the inradius as 3.9… is it correct??????????
Girish, yes 3.8xx is what it comes I think, don’t remember exactly. And true, the ticket window should not have any change to begin with. For the third guy to be the first to wait, the first guy has to have a 1 rupee (since if the first guy has a 2 rupee, he will be the first to wait), and the second has to have a 2 rupee (since if the first and second both have 1 rupee, the third guy will not have to wait. The third guy will now need to have a 2 rupee. So we can calculate the probability accordingly. For the 5th guy it is a lot more complicated though…
regards
J
Unwrite series is the best series amongst the entire material that you’ve posted till now 🙂
And especially for me, this is amazing because I always go through your website whenever I am traveling and thus I have to ‘un-write’ anyways 😀
Ratish, thanks for the kind words. I am glad it is proving to be of help.
I believe that these methods are also the most useful in the actual exam – not for the majority of questions, but if you can do even a couple of questions without writing, it gives a tremendous morale boost. And anyone can learn how to do this really, all it takes is the right mindset (instead of the write mindset 😉 )…and a lot of practice! The bonus is that trying this in practice also forces you to strengthen your basic concepts….
regards
J
Exactly.
I spend 2 hours daily travelling (back and forth) and hence I always try to solve the questions on your website and other CAT related websites mentally. And it really helps!
I believe the best preparation for CAT is not by learning formulae or studying numerous hours a day, but by making your brain actually think and to keep it ticking everyday. 🙂
Sir what would be the answer and approach in question 2 if it would have been 19 successive discounts instead of 20 ?
Vaibhav, in that case it would be a truly nasty problem, with horrendous calculations – but one that would never be asked in a CAT. The thing is, if you see something with such calculations, you should recognise that there must be a trick.
Remember that in an exam like the CAT, they are trying to differentiate good candidates from bad. A question which everybody could answer would be useless to them – but so would one which nobody could answer!
regards
J
It is not fair of the ticket window guys not keeping the change. 😛
True, but then life is rarely fair, is it?
regards
J
Hie,
In the ticket window question, all the arrangements of children are equally likely. So we can have a situation in which each of the 9 children ahead of the 10th child has Re 1 with them and the 10th child is the first one to have Rs 2. In that situation won’t the 10th child be the first one to wait? What am i missing?
If the first 9 kids have given Re 1 each, then why would the 10th have to wait? There is now plenty of change with the ticket counter operator!
regards
J
In the last question, the triangle is 8,15,17 which is a Right angled traingle
so incircle would be a+b-c/2 which is 3
right?
8, 15, 17 are the altitudes not the sides…
regards
J