@anurag_chauhan The last sum is some sort of miscalculation I guess, because according to the sum when y=1 then x = 1 * 6 and not vice versa. In that case the value of y extends upto 100 and x upto 496*501 for which the ans should be 501.

Q 30) If a,b,c are the roots of the eqn x^3+4x+1= 0 ,then the value of 1/(a+b) + 1/(b+c) +1/(c+a) ?