04-03-09 Probability

Find the probability that the points two randomly chosen numbers in [0,1] are such that the distance between them is less than 1/2

If you remember a similar question of time that two friends meet you can solve it in a flash

Then try to solve the question that 3 points are given.. probability that all three have distance between them as less than 1/2!

28 Answers

62
Lokesh Verma ·

If you dont want / cant solve by finding the figure then do one thing

take a fixed value of z and find the area of the layer

then integrate..

13
Двҥїяuρ now in medical c ·

bhaiya how to solve this question.....

Find the probability that 4 randomly chosen numbers in [0,1] are such that the distance between them is less than 1/2

any hint.....

any alternative way...other than 4 dimensions

13
Двҥїяuρ now in medical c ·

try to find area of that shaded area in terms of z....length of the red line is (0.5-z)

21
tapanmast Vora ·

Abhi, can u pl. xplain ur Integration expression in mor detail!!! i dint get it [2]

13
Двҥїяuρ now in medical c ·

but is it possible??...4 dimension case seems interesting[12]

any alternative way....??

62
Lokesh Verma ·

@abhirup..

there is a generalization to n dimensions..

but I am sure that it will be very difficult to first visualise and then solve it for even the 4 dimension case..

13
Двҥїяuρ now in medical c ·

Then.....

how to find the probability if more than three points are chosen....
we don't have more than three dimensions[7]

[12]

13
deepanshu001 agarwal ·

1/4 is d ans.....

62
Lokesh Verma ·

Yes then it seems to be awesome :)

let me do the final calculations to see if our answers do match :)

13
Двҥїяuρ now in medical c ·

i did 2*∫...that....dz

as the lower part and upper part has same volume....

62
Lokesh Verma ·

abhirup explain this.. why is z integral in your expression only between 0 and 1/2??

13
Двҥїяuρ now in medical c ·

edited my pic

anyone... verify this one....

13
Двҥїяuρ now in medical c ·

the area of the shaded layer....[0.5+z]2-(1/2)*2z2

13
Двҥїяuρ now in medical c ·

is the ans 1/2[7]
2\int_{0}^{0.5}{[(0.5+z)^2 -z^2}]dz

62
Lokesh Verma ·

PS: Inspired from http://targetiit.com/iit_jee_forum/posts/probability_donno_if_already_done_3248.html

21
tapanmast Vora ·

yah matie..... sample space to pata chal gai........

I m struggling to find da shape of the FAVOURABLE CASES volume

39
Dr.House ·

Take the cube with one corner [0,0,0] and another [1,1,1] with side , parralel to axes. Now any point in this cube correspond to a choice of 3 points on the segment [0,1]

21
tapanmast Vora ·

INTERESTING [12]

KABHI LOCUS IN 3-D ke bare mein zyada socha nahi.....

62
Lokesh Verma ·

now how do you generalise to the 3 variable case where we have each of

|x-y|<1/2
|x-z|<1/2
|y-z|<1/2

33
Abhishek Priyam ·

=shaded area/total area of square
=(3/4)/1

24
eureka123 ·

favourable=mod(x-y)<1/2

21
tapanmast Vora ·

can u pl. add/explai the range of values our two chosen numbers can take......

13
Двҥїяuρ now in medical c ·

bhaaiya...can u give the link of that one....

21
tapanmast Vora ·

Sir, but wat abt our answers are they both wrong?

62
Lokesh Verma ·

do you guys remember that problem where we did that 2 friends would come and stay for 15 minutes.. between 5 to 6 PM?

This has a very similar logic! (If you can feel that!)

21
tapanmast Vora ·

Can u pl. xplain this que : as in wats da range of values of pts. (in terms of dis. b/w em etc.)

Then try to solve the question that 3 points are given.. probability that all three have distance between them as less than 1/2!

13
Двҥїяuρ now in medical c ·

1/2[7]

21
tapanmast Vora ·

Is the ans to this : Find the probability that the points two randomly chosen numbers in [0,1] are such that the distance between them is less than 1/2

= pi(0.5)2/ pi(1)2
= 1/4 [7]

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