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Question

A and B can complete a work in 12 days and 6 days, respectively. They started doing the work together but after 2 days, B had to leave, and A completed the remaining work alone. The remaining work was completed in ________ days.

The correct answer is
6

Work Rate Analysis for A and B

First, determine the daily work rate for both individuals.

  • A completes the work in 12 days, so A's daily rate is $ \frac{1}{12} $.
  • B completes the work in 6 days, so B's daily rate is $ \frac{1}{6} $.

Combined Work and Remaining Work

Calculate the work done when they work together and the remaining portion.

  • Their combined daily rate is $ \frac{1}{12} + \frac{1}{6} = \frac{1}{12} + \frac{2}{12} = \frac{3}{12} = \frac{1}{4} $ of the work.
  • In the 2 days they worked together, they completed $ \frac{1}{4} \times 2 = \frac{1}{2} $ of the work.
  • The remaining work is $ 1 - \frac{1}{2} = \frac{1}{2} $.

A Completes Remaining Work

Determine the time A needs to finish the rest of the work alone.

  • A's daily rate is $ \frac{1}{12} $.
  • Time for A to complete the remaining $ \frac{1}{2} $ work = $ \frac{1/2}{1/12} $.
  • Calculation: $ \frac{1}{2} \times 12 = 6 $ days.

A completed the remaining work in 6 days.

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Important Questions from Time & Work (Notes)

  1. A fresh water tap fills a fish tank in 40 minutes. The same tank is filled by a salt water tap in 120 minutes. If both the taps are open, how many minutes will it take to fill the tank?
  2. A completes $\frac{7}{10}$ of a work in 15 days and then he completes the remaining work with the help of B in 5 days. In how many days can A and B together complete the entire work?
  3. Aman can do 50% of the job in 16 days, and Bhanu can do 25% of the job in 24 days. In how many days can they do $\frac{1}{4}^{th}$  of the job working together ?

  4. X can finish a job in $141$ days. He worked for $57$ days alone and the remaining work was completed by Y, in $84$ days. How many days would both together take to complete the entire job?
  5. Ravina, Sujata, and Saroj can complete a work of painting separately in 32, 48, and 64 hours, respectively. They started working together, but Saroj left after 5 hours. From the 6th hour, Ravina and Sujata decided to work on alternate hours starting with Ravina. In how much time will the entire work of painting be completed?

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