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.

#Combinatorics

Easy Math Editor

This discussion board is a place to discuss our Daily Challenges and the math and science related to those challenges. Explanations are more than just a solution — they should explain the steps and thinking strategies that you used to obtain the solution. Comments should further the discussion of math and science.

When posting on Brilliant:

Use the emojis to react to an explanation, whether you're congratulating a job well done , or just really confused .
Ask specific questions about the challenge or the steps in somebody's explanation. Well-posed questions can add a lot to the discussion, but posting "I don't understand!" doesn't help anyone.
Try to contribute something new to the discussion, whether it is an extension, generalization or other idea related to the challenge.
Stay on topic — we're all here to learn more about math and science, not to hear about your favorite get-rich-quick scheme or current world events.

Markdown	Appears as
`italics` or `_italics_`	italics
`bold` or `__bold__`	bold
- bulleted - list	bulleted list
1. numbered 2. list	numbered list
Note: you must add a full line of space before and after lists for them to show up correctly
paragraph 1 paragraph 2	paragraph 1 paragraph 2
`[example link](https://brilliant.org)`	example link
`> This is a quote`	This is a quote
# I indented these lines # 4 spaces, and now they show # up as a code block. print "hello world"	# I indented these lines # 4 spaces, and now they show # up as a code block. print "hello world"

Math	Appears as
Remember to wrap math in `$` ... `$` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$

Comments

Is the answer 42/347?

Rajorshi Chaudhuri - 6 years, 3 months ago

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

Kyle Finch - 6 years, 3 months ago

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

Tanishq Varshney - 6 years, 3 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.

Rajorshi Chaudhuri - 6 years, 3 months ago

@Rajorshi Chaudhuri – ok! now i understood, thanx :)

Tanishq Varshney - 6 years, 3 months ago

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

Rohit Shah - 6 years, 3 months ago

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

Tanishq Varshney - 6 years, 3 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$