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Time and Work

Chain Rule: Learn Concept and Tricky Questions

In this video, we learn the concept of Chain Rule in detailed with two very important tricky questions.

[1] 40 carpenters working 8 hours a day can make 20 chairs in 60 days. After 30 days, an order of 10 more chairs came. To complete the total work on time, how many more hours per day they will have to work? 

X can build up a wall in 8 days and Y can break it in 3 days

X can build up a wall in 8 days and Y can break it in 3 days. X has worked for 4 days and then Y joined to work with X for another 2 days only. In how many days will X alone build up the remaining part of the wall?

    (A) 7 1/3 days

    (B)  6 days

    (C)  8 days 

A, B and C are entrusted with a task. B needs 3 hours more to cope with the job then B and C working together. A working alone would need as much time as B and C working together. A working alone would spend 8 hours less than the double period of time B..

A, B and C are entrusted with a task. B needs 3 hours more to cope with the job then B and C working together. A working alone would need as much time as B and C working together. A working alone would spend 8 hours less than the double period of time B would spend working alone. How much time would A, B and C need to complete the task if they all worked together?

1 man 3 women and 4 boys can do a piece of work in 96 hours, 2 men and 8 boys can do it in 80 hours, 2 men and 3 women can do it in 120 hours. 5 men and 12 boys can do it in:

1 man, 3 women and 4 boys can do a piece of work in 96 hours, 2 men and 8 boys can do it in 80 hours, 2 men and 3 women can do it in 120 hours. 5 men and 12 boys can do it in:

(A) 39 1/11

(B)  42 7/11

(C)  43 7/11

(D)  44

A task can be completed in 20 days, if A and B work together.

A task can be completed in 20 days, if A and B work together. However, if A worked alone and completed half the task and then B takes over and completes the second half, the task will be completed in 45 days. How long will A take to complete the task if she worked alone? Assume that B is more efficient than A.

(A) 25 days

(B) 30 days

Ramesh can do a Maths assessment consisting of 100 questions alone in 4 hours.

Ramesh can do a Maths assessment consisting of 100 questions alone in 4 hours. Ramesh's friends Surbhi and Alka together can do the same set of questions at 1/3 speed of Ramesh. Pintu and Depak together can do the same set of questions at 1/5 speed of Ramesh. If the five of them do a set of 230 questions together, in how much time can they complete the questions

(A) 360 minutes

(B) 580 minutes

(C) 300 hours

Ashok can do some work in 10 days, Mohan in 20 days and Vijay can do it in 25 days.

Ashok can do some work in 10 days, Mohan in 20 days and Vijay can do it in 25 days. They start working in turns with Ashok starting to work on the first day, Mohan on the second day and Vijay on the third day and so on. They work in this way for 12 days. After this, Vijay is replaced by Sohan who can complete the work in 20 days by himself. Find the time taken to complete 96% of the work.

A tap can fill a tank in 10 hours. After opening the tank for 5 hours

A tap can fill a tank in 10 hours. After opening the tank for 5 hours it was found that a small outlet at the bottom of the tank was open and water was leaking through it. It was then immediately closed. It took 7 hours to fill the tank after closing the outlet. What time will be taken by the outlet to empty the full tank of water?


(A) 20 H

(B) 25 H

(C) 30 H

Z is 40% less efficient than X. X and Y together can finish a piece of work in 10 days.

Z is 40% less efficient than X. X and Y together can finish a piece of work in 10 days. Y and Z together can do it in 15 days. In how many days can X alone finish the same piece of work?

(A) 12

(B) 15

(C) 20

(D) Can't be determined

(E) None of these

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