Let n 1   a n d   n 2 be the number of red and black balls, respectively, in box I. Let n 3 a n d…

Let n1 and n2 be the number of red and black balls, respectively, in box I. Let n3and n4 be the number of red and black balls, respectively, in box II.
One of the two boxes, box I and box II, was selected at random and a ball was drawn randomly out of this box. The balls was found to be red. If the probability that this red ball was drawn from box II is 13 , then the correct option(s) with the possible values of n1, n2, n3and n4 is(are)
  1. n1=3, n2=3, n3=5, n4=15
  2. n1=3, n2=6, n3=10, n4=50
  3. n1=8, n2=6, n3=5, n4=20
  4. n1=6, n2=12, n3=5, n4=20

Solution



13= 12n3n3+n412 n1n1+n2+ n3n3+n4
13= n3n3+n4n1n1+n2+ n3n3+n4
(i)  RHS 520520+36= 1414+12= 141+24=13
(ii) RHS 10601060+39=1616+13= 1612=13
(iii) 525814+525= 1547+15= 1520+735=727
(iv) 525618+525= 155+315= 15815=15×158=38 .

Asked in: JEE Advanced 2015 (Paper 2)

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