In a test of 80 questions, Jyothsna answered 75% of the first 60 questions correctly. What % of the remaining questions she has to answer correctly so that she can secure an overall percentage of 80 in the test?
a. 80%                         b. 90%             c. 85%             D. 95%                                              
Solution
[(75% X 60) + (x% X 20)] / 80 = 80%  =>  x = 95.   (since required is 80%)
(OR)  60 out of 80 is 3/4. So,  (3/4 X 75)  +  (1/4 X x)  = 80  =>  x =95.