UPSC Maths Challenge : A Problem A Day! (Day 24)

I apologize for I could not do more than this short post today but the problem included is indeed very interesting.You look at it and try to think of two variables and that will be the most fatal decision of your life.I have used a simple trick for solving this,which you have to read on to find out.Hope this helps.

(Original Photograph Source)

Today's Problem(25/07/2015)

Questions Credit : http://www.m4maths.com

A candidate attempted 12 questions and secured full marks in all of them. If he obtained 60% in the test and all questions carried equal marks, then what is the number of questions in the test? [UPSC 2010 (CS-P)]

a) 36

b) 30

c) 25

d) 20

Let us assume that the full marks is 100 and that each question carries x marks.Therefore,according to the information given in the question,we have 12 * x = 60

or x = 5.So,the number of questions left is (100 - 60)/5 = 8.

Therefore,the total number of questions is 12 + 8 = 20.