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Probability can be a real fun to solve and scoring topic too but only when right approach is used. A wrong approach can take you far from the answer. Its Probability is much more a case to be thought practically rather than jumping here and there with equations. Probability of solving questions on this topic is inversely proportional to the probability of your losing concentration. So check your concentration.....

Problem :
From a pack of n cards no 1,2,3,4,5.......... n. A draws a card and then puts it back. Now B draws a card. Find the probability that B has drawn the same card as A.
Solution :
A can draw card in n ways.
Similarly, B can also draw card in n ways.
So the total no ways in which A and B can select a card is = n x n.
This becomes the total no of possible cases.

Now A and B can draw the same card nos like in these cases(1,1) or (2,2) or (3,3) or (4,4)....... or (n,n). Hence the total no of favourable cases are n.

So P = No of favourable cases / Total no of cases = n/(nxn) = 1/n

That was quite a simple problem. But the important thing to consider is that how you start to think. If you start with a negative approach of  " its too difficult ..very hard problem... bla bla bla....", it oughts to become the same.  So be positive and explore the ways to achieve the desired results.

Your suggestions and querries are welcome.
Mail to mathsprobe@gmail.com

IIT JEE EXAM 2011- EXAM DATE 10 April 2011, Last date to Apply = 15 December 2010

1 comment:

  1. The questions on Cards and aces are so much confusing in the Exams. I dont feel like giving it a try.