In cat entrance examination paper there are 3 sections, each containing 5 questions. a candidate has to solve 5,
choosing at least one from each section. the number of ways he can choose is
op 1: 2,500
op 2: 2,250
op 3: 2,750
op 4: 3,250

The best and most correct answer providedfrom your question about the entrance examination paper is the second option which is 2,250. The problem can be solved by:

3-1-1 : 5c3*5c1*5c1 *3!/2! = 750 
2-2-1 : 5c2*5c2*5c1 *3!/2! = 1500

Adding the two answers:

750 + 1500 = 2250

I hope it has come to your help.