Your primers allowed you to amplify a 2 Kbp sequence You dig

Your primers allowed you to amplify a 2 Kbp sequence. You digest the amplicon and 100ng of the vector with the appropriate enzymes in order to clone the sequence of interest. How much of the digested amplicon should be added to the ligation mix in order to have an insert to vector ration of 3:1? The answer is 200ng, Please explain how to get this answer

Solution

ng of insert = (ng of vector x kb size of the insert)/kb size of the vector x insert to vector ratio

Size of the vector is missing, I am taking this 3 Kb, size of standard TA cloning vectors.

ng of insert = (100ng x 2 Kb) / 3Kb x 3/1 = 200ng