Indian Institute of Foreign Trade 2010 Solved Paper

let G be number of days in which Dr. gupta can complete the evaluation of answer sheet , let Sh be number of days in which Dr. Sharma can complete the evaluation of answer sheet , let Si be number of days in which Dr. Singh can complete the evaluation of answer sheet
Given Dr. Gupta is 40% more efficient than Dr. Sharma therefore number of days required by Dr. Sharma to complete the evaluation of answer sheet = 1.4×G
Dr. Gupta takes 10 days less than Dr. Sharma to complete the evaluation work i.e. 1.4G-G = 10 therefore G = 25 and hence Sh = 35
Also given that Dr. Sharma is 20% more efficient than Dr. Singh therefore number of days required by Dr. Singh to complete the evaluation of answer sheet $=\frac{35}{1.2}=42$i.e $\mathit{S}\mathit{i}=42$
Dr. Gupta starts the evaluation work and works for 10 days therefore he completes $\frac{10}{25}$ of work then Dr. Sharma takes over. Dr. Sharma evaluates for next 15 days therefore he completes $\frac{15}{35}$ of work. Fraction of work left is $1-\frac{10}{25}-\frac{15}{35}=\frac{6}{35}$ now time required by Dr. Singh to complete this amount of work is $\frac{6\times 42}{35}=7.2$days
Therefore our answer is option 'A'