# Help needed!!

Plz i request u to post a solution for this as I don't know the correct answer

A bag contains 3 maths books and 2 physics books. A book is drawn at random, if it is of maths, 2 more books of maths together with this book put back in the bag and if it is of physics it is not replaced in the bag.This experiment is repeated 3 times.If third draw gives maths book,what is the probability that first two drawn books were of physics.

Note by Tanishq Varshney
3 years, 6 months ago

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We have to use Bayes theorem right ? Calculate probability for the four events separately like MMM , MPM , etc. It will be a messy answer

- 3 years, 6 months ago

ya u r correct,its a question from one of my friends quiz test paper

- 3 years, 6 months ago

- 3 years, 6 months ago

i guess it should be $$\frac{42}{357}$$ which is equal to $$\frac{2}{17}$$

- 3 years, 6 months ago

i don't know the answer @Rajorshi Chaudhuri .. can u post ur method in brief

- 3 years, 6 months ago

I solved it as: Let math book be M and physics book be P. So the last book is M and it can be with MMM, MPM, PMM, PPM. Now, P(MMM)=(3/5)(5/7)(7/9)=1/3. Similarly for the rest. And out of this we need PPM.

- 3 years, 6 months ago

ok! now i understood, thanx :)

- 3 years, 6 months ago