उत्तर : 2. "40"
व्याख्या :

Answer: B) 40 Explanation: The third proportional of two numbers p and q is defined to be that number r such that p : q = q : r.   Here, required third proportional of 10 & 20, and let it be 'a' => 10 : 20 = 20 : a 10a = 20 x 20 => a = 40   Hence, third proportional of 10 & 20 is 40.