Rationalization method is to be used while solving sums like these
Rationalization factor for :
1) 1/√a ------> √a
2) a + √b -------> a - √b
3) a - √b ---------> a + √b
4) √a + √b ----------> √a - √b
5) √a - √b ------------> √a + √b

516 / √682
As seen in above Rationalization Methods we can use 1^st rule to solve the problem
Thus 516 / √682 is multiplied the rationalizing factor i.e. √682
To balance the extra added rationlizing factor we multiply the given ratio by √682 / √682
Thus the result of (516 / √682) * (√682 / √682) = (516 * √682) / 682
Thus 516 / √682 = (516 * √682) / 682 = 19.758661191541
Thus 516 / √682 = (516 * √682) / 682 = 20(round off to nearest integer)