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)
Abhijeet Gaurav Best Answer
Answer is (C). First amino acid can take 20 as there are 20 types of Amino acids. Similarily 2nd Amino acids can take 20 types of Amino acids. But once you choose first and second then you don't have option at 3rd and 4th as you they are repetitive.