Time and Work Questions

FACTS  AND  FORMULAE  FOR  TIME  AND  WORK  QUESTIONS

 

 

1. If A can do a piece of work in n days, then A's 1 day's work =1n

2. If A’s 1 day's work =1n, then A can finish the work in n days.

 

3. A is thrice as good a workman as B, then:

Ratio of work done by A and B = 3 : 1.

Ratio of times taken by A and B to finish a work = 1 : 3.

 

NOTE : 

Efficiency1No of time units

 

 Efficiency × Time = Constant Work

 

Hence, Required time = WorkEfficiency

 

Whole work is always considered as 1, in terms of fraction and 100% , in terms of percentage.

In general, number of day's or hours = 100Efficiency

Q:

Two pipes A and B can fill a tank in 24 hours and 1717 hours respectively. Harihar opened the pipes A and B to fill an empty tank and some times later he closed the taps A and B , when the tank was supposed to be full. After that it was found that the tank was emptied in 2.5 hours because an outlet pipe "C" connected to the tank was open from the beginning. If Harihar closed the pipe C instead of closing pipes A and B the remaining tank would have been filled in :

A) 2 hours B) 8 hours
C) 6 hours D) 4 hours
 
Answer & Explanation Answer: B) 8 hours

Explanation:

Efficiency of Inlet pipe A = 4.16%       10024 

 

Efficiency of Inlet pipe B = 5.83%      1001717  

 

Therefore, Efficiency of A and B together = 100 %   

 

Now, if the efficiency of outlet pipe be x% then in 10 hours the capacity of tank which will be filled = 10 *  (10 - x)

 

Now, since this amount of water is being emptied by 'C' at x% per hour, then

 

 10x10-xx=2.5 hrs 

 => x = 8 

 

Therefore, in 10 hours 20% tank is filled only. Hence, the remaining 80% of the  capacity will be filled by pipes A and B  in 80/10 = 8 hours 

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Q:

There are three boats B1, B2 and B3 working together they carry 60 people in each trip. One day an early morning B1 carried 50 people in few trips alone. When it stopped carrying the passengers B2 and B3 started carrying the people together. It took a total of 10 trips to carry 300 people by B1, B2 and B3. It is known that each day on an average 300 people cross the river using only one of the 3 boats B1, B2 and B3. How many trips it would take to B1, to carry 150 passengers alone?

A) 15 B) 30
C) 25 D) 10
 
Answer & Explanation Answer: A) 15

Explanation:

Combined efficiency of all the three boats = 60 passenger/trip 

 

Now, consider option(a)

 

15 trips and 150 passengers means efficiency  of B1 =  10 passenger/trip 

 

which means in carrying 50 passengers B1 must has taken 5 trips. So the rest trips equal to 5 (10-5 = 5) in which B2 and B3 together carried remaining 250 (300 - 50 = 250) Passengers.

 

Therefore the efficiency of B2 and B3 = 250/5 = 50 passenger/trip  

 

Since, the combined efficiency of B1, B2 and B3 is 60. Which is same as given in the first statement hence option(a) is correct.

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33 10812
Q:

If 6 men and 8 boys can do a piece of work in 10 days while 26 men and 48 boys can do the same in 2 days what is time taken by 15 men and 20 boys?

A) 4 days B) 6 days
C) 7 days D) 5 days
 
Answer & Explanation Answer: A) 4 days

Explanation:

Given that 

6 men and 8 boys can do a piece of work in 10 days 

26 men and 48 boys can do the same in 2 days

 

As the work done is equal,

10(6M + 8B) = 2(26M + 48B)

60M + 80B = 52M + 96B

=> M = 2B

=> B = M/2 ……(1)

 

Now Put (1) in 15M + 20B

=> 15M + 10M = 25M

Now, 6M + 8B in 10 days

=> (6M + 4M) 10 = 100M

Then D(25M) = 100M

=> D = 4 days.

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32 23106
Q:

A, B and C can complete a piece of work in 24,6 and 12 days respectively.Working together, they will complete the same work in:

A) 1/24 days B) 7/24 days
C) 24/7 days D) 4 days
 
Answer & Explanation Answer: C) 24/7 days

Explanation:

(A+B+C)'s 1 day's work = (1/24 + 1/6 + 1/12) = 7/24

so, A,B and C together will complete the work in 24/7 days.

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32 16130
Q:

A and B together can do a piece of work in 40 days. A having worked for 20 days, B finishes the remaining work alone in 60 days. In How many days shall B finish the  whole work alone?

A) 60 B) 70
C) 80 D) 90
 
Answer & Explanation Answer: C) 80

Explanation:

Let A's 1 day's work=x and B's 1 day's work=y

Then x+y = 1/40 and 20x+60y=1 

Solving these two equations , we get : x= 1/80 and y= 1/80

Therefore B's  1 day work = 1/80

Hence,B alone shall finish the whole work in 80 days

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31 22995
Q:

When A, B and C are deployed for a task , A and B together do 70% of the work and B and C together do 50% of the work. who is most efficient?

A) A B) B
C) C D) can't be determined
 
Answer & Explanation Answer: A) A

Explanation:

A + B= 70%   

B + C =50%   

  (A+B)+(B+C)-(A+B+C)= B

=> B= 20%     A= 50%        and   C=30%

Hence A is most efficient

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31 17650
Q:

Amit can do a piece of work in 45 days, but Bharath can do the same work in 5 days less, than Amit, when  working alone. Amit and Bharath both started the work together but Bharath  left after some days and Amit finished the remaining work in 56 days with half of his efficiency but he did the work with Bharath with his complete efficiency. For how many days they had worked together?

A) 6 B) 8
C) 9 D) 12
 
Answer & Explanation Answer: B) 8

Explanation:

    AmitBharatNo.of Days4540Efficiency2.22Percent(=145)2.5 Percent(=140)

 

Amit did the work in 56 days = 56×145×2=2845 

 

Therefore, Rest work 17/45 was done by Amit and Bharath = 174517360 = 8 days

 

 

 

( since Amit and Bharath  do the work in one day = 145+140=17360)

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30 13901
Q:

A can finish a work in 18 days and B can do the same work in half the time taken by A. then, working together, what part of the same work they can finish in a day ?

A) Total work B) One-fourth work
C) Half work D) Two-third work
 
Answer & Explanation Answer: C) Half work

Explanation:

A can do the work = 18 days
B can do the work = 18/2 = 9 days
(A + B)'s 1 day work = 1/18 + 1/9 = 1/6
=> In 3 days = 3x1/6 = 1/2 work is completed.

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