Quantitative Aptitude Ques 1300

Question: Working together A and B can complete a piece of work in 5 days. If A had worked twice as fast the work would have been completed in 4 days. In how many days can A alone complete the work?

Options:

A) $ 20days $

B) $ 6\frac{2}{3}days $

C) $ 18days $

D) $ 6\frac{1}{4}days $

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Answer:

Correct Answer: A

Solution:

  • Let A do the work in a days.

$ \therefore $ A’s 1 day’s work $ =\frac{1}{a} $ Let B do the work in b days,

$ \therefore $ B’s 1 day’s works $ =\frac{1}{b} $ According to the question, $ \frac{1}{a}+\frac{1}{b}+\frac{1}{5} $ … (i) $ \frac{2}{a}+\frac{1}{b}=\frac{1}{4} $ … (ii) On solving Eqs. (i) and (ii)i we get

$ \Rightarrow $ $ \frac{1}{a}-\frac{2}{a}=\frac{1}{5}-\frac{1}{4} $

$ \Rightarrow $ $ \frac{1-2}{a}=\frac{4-5}{20} $

$ \Rightarrow $ $ -\frac{1}{a}=-\frac{1}{20} $

$ \Rightarrow $ $ \frac{1}{a}=\frac{1}{20} $

$ \Rightarrow $ $ a=20days $