CAT 2025 Lesson : Time & Work - Concepts & Cheatsheet

Note: The video for this module contains a summary of all the concepts covered in the Time & Work lesson. The video would serve as a good revision. Please watch this video in intervals of a few weeks so that you do not forget the concepts. Below is a cheatsheet that includes all the formulae but not necessarily the concepts covered in the video.

8. Cheatsheet

1

) Worker-Days Method: This is used when there are many people in a group who work at the same rate (or efficiency). Here, we use units such as worker-days, man-hours, etc.

2

) Unitary Method: This method is used for solving all other types of questions. Here, we assign the total work as 1. We use efficiencies to solve the problems.

3

) Portion of work completed in a day and time taken have a reciprocal relationship. For example, if John can complete a piece of work in

20

days, then his efficiency is the portion of work he can complete in

1

day, which is

\dfrac{1}{20}^{th}

of the work.

4

) If the efficiency becomes

\bm{x}

times the initial efficiency, then the time taken becomes

\dfrac{\bm{1}}{\bm{x}}

times the initial time taken.

5

) If the ratio of efficiencies of A and B is

a : b

, then the ratio of time taken by them is

b : a

6

) In case of leaks which have negative rate of completion, the efficiency is negative.

7

) When groups work alternately, we use the parts method to solve.

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