How to approach a problem? Break the problem solving processes into steps. Problem: Number S is obtained by squaring the sum of digits of a twodigit number D. if difference between S and D is 36, then the twodigit number D is a. 54 b. 36 c. 45 d. 24 When you analyze the above question, What do you see? 1. S is a two digit number( How do you represent a two digit number algebraically) 2. Is S>D or is D>S? Next convert the number into an equation. A two digit number can be represented as D =10x+y ( x is the tens digit and y is the units digit) S = x^2+y^2 SD =36 or DS =36. Solution process Test aspirants usually opt for many process to arrive at an answer. We have listed two process to solve this problem. Either you can solve the above equations x^2+y^2  (10x+y) = 36 Or You can use the answer options and check which answer option fits the given equation. Either way you will get 45 as the answer. Working with answer options is an effective problem solving strategy. 
