Quantitative Aptitude Ques 22

Question: A can do a work in 10 days and B in 20 days. If they together work on it for 5 days, then the fraction of the work that is left, is

Options:

A) $ \frac{3}{20} $

B) $ \frac{4}{3} $

C) $ \frac{1}{4} $

D) $ \frac{3}{4} $

Show Answer

Answer:

Correct Answer: C

Solution:

  • Work done by A in one day $ =\frac{1}{10} $ Work done by B in one day $ =\frac{1}{20} $ Total work done by $ (A+B) $ in one day $ =\frac{1}{10}+\frac{1}{20}=\frac{2+1}{20}=\frac{3}{20} $ Work done by $ (A+B) $ in 5 days $ =\frac{3}{20}\times 5=\frac{15}{20}=\frac{3}{4} $

$ \therefore $ Fraction of the work that is left $ =1-\frac{3}{4}=\frac{1}{4} $ Alternate Method Work done in 1 day by A and B $ B=\frac{20+10}{200}=\frac{30}{200}=\frac{3}{20} $ Then, work completed in 5 days $ =\frac{3}{20}\times 5=\frac{3}{4} $ Left work $ =1-\frac{3}{4}=\frac{1}{4} $