GMAT Book 2: Rates: Work Time

Pipes - cisterns and work - time will account for about 1 or 2 questions in the GMAT math section. Questions from this topic appear in both variants - problem solving and data sufficient. Often times, these questions will appear as word problems in algebra.

Syllabus Covered in Wizako's GMAT Book | Time and Work, Pipes and Cisterns

A typical question that appear from this topic in the GMAT quant section is a word problems. The core idea covered in this chapter is similar to the one covered in Speed Time Distance. So, if you have a good grasp of Speed Time Distance, you will be able to understand and solve questions in this topic with a lot of ease. Wizako's GMAT Math Lesson Book in this chapter covers the following concepts:

1. The chapter starts by explaining the relation between the time taken to complete a task (fill a tank) and rate at which the task is completed with illustrative examples. The reciprocal relation between time and fraction of work completed is explained in depth.
2. There are 17 solved examples in questions related to pipes and cisterns. Some of the tough math questions in this topic are featured here.
3. How to frame equations for work time questions when time taken to complete a task is provided?
4. There are 14 solved examples for questions related to work and time. Shorcuts to few hard math questions in work time are provided.
5. 24 exercise problems, 12 each in pipes & cisterns and work & time have been provided with the answer key and explanatory answers.
6. A multiple choice test with 35 GMAT level questions with explanatory answers and answer key is provided in the Math work book.

Here is a typical solved example in Wizako's GMAT Book from this chapter

Sample Question

Pipe A fills a tank in 30 minutes. Pipe B can fill the same tank 5 times as fast as pipe A. If both the pipes were kept open when the tank is empty, in how many minutes will the tank be filled?

Explanatory Answer

Pipe B fills the tank 5 times as fast as pipe A.
Therefore, pipe B will fill the tank in one-fifth of the time that pipe A takes.

Pipe B will fill the tank in \\frac{30}{5}) = 6 minutes. In 1 minute, pipe A will fill \\frac{1}{30}^{th}) of the tank and pipe B will fill \\frac{1}{6}^{th}) of the tank.
Therefore, together, the two pipes will fill \\frac{1}{30}) + \\frac{1}{6}) = \\frac{1 + 5}{30}) = \\frac{6}{30}) = \\frac{1}{5}^{th}) of the tank in a minute

Hence, the two pipes working together will take 5 minutes to fill the tank.

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