Time management is very much important in IIT JAM. The eduncle test series for IIT JAM Mathematical Statistics helped me a lot in this portion. I am very thankful to the test series I bought from eduncle.
Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Ruby negi
I used this formula in this ques.. because divergence of r cap/r^2 =4π* dirac Delta... if you don't use this ,you will get wrong solution.. this is exceptional case..