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:

A can complete a piece of work in 12 days and B is 60% more efficient than A. In how many days B will complete the same work  ?

A) 8.7 hrs B) 5.2 hrs
C) 5 hrs D) 7.5 hrs
 
Answer & Explanation Answer: D) 7.5 hrs

Explanation:

Ratio of times taken by A and B = 160 : 100
A can do the work in 12 days
Let B can do the work in "D" days
=> 160:100 = 12 : D
=> D = 12 x 100/160 = 7.5 hrs

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Q:

M can complete a piece of work in 10 days. N is 33.33% less efficient than M. calculate the number of days required to both to complete the work?

A) 6 days B) 8 days
C) 11 days D) 13 days
 
Answer & Explanation Answer: A) 6 days

Explanation:

M = 10 days

The ratio of efficiency of M & N are 3 : 2

Hence, the time rquired for N alone = 15 days

=> Required time taken t=by both to complete the work = M x N / M + N 

= 10 x 15/ 10 + 15

= 150/25

= 6 days.

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Q:

A can do a piece of work in 15 days and B can do it in 16 days and C can do it 24 days. They started the work together and A leaves after 3 days and B leaves after 4 days from the beginning. How long will work lost ?

A) 10 2/3 days B) 13 1/5 days
C) 12 2/3 days D) 11 5/7 days
 
Answer & Explanation Answer: B) 13 1/5 days

Explanation:

3/15 + 4/16 + x/24 = 1

x=1315

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Q:

It takes one minute to fill 2/7 th of a vessel. What is the time taken in minutes to fill the whole of the vessel  ? 

A) 1/7 min B) 7/2 min
C) 5/7 min D) 7/5 min
 
Answer & Explanation Answer: B) 7/2 min

Explanation:

Time taken to fill 2/7 = 1
Then to fill full 1 = ?
? = 1/(2/7) = 7/2 minutes.

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Q:

Relation Between Efficiencies

6 boys and 8 girls finish a job in 6 days and 14 boys and 10 girls finish the same job in 4 days. In how many days working together 1 boy and 1 girl can finish the work?

Answer

Sol : In this kind of questions we find the work force required to complete the work in 1 day (or given unit of time) then we equate the work force to find the relationship between the efficiencies (or work rate) between the different workers.


 


Therefore, 6B+8G = 6 days


 => 6(6B+8G)= 1 day  (inversely proportional)


 => 36B+48G =1         ( by unitary method)


 


Again  14B+10G = 4days


 => 56B+40G =1


 


so, here it is clear that either we employ 36B and 48G to finish the work in 1 day or 56B and 40G to finish the same job in 1 day. thus , we can say


 => 36B+48G = 56B+40G


 => G= 2.5B


Thus a Girl is 2.5 times as efficient as a boy.


 


Now, since  36B+48G = 1


 => 36B+48(2.5 B)=1


 =>156B=1


i.e., to finish the job in 1 day 156 boys are required or the amount of work is 156 boys-days


 


Again    1G+1B=2.5B+1B=3.5B


 


Now, since 156 boys can finish the job in 1 day


so 1 boy can finish the job in 156 days


Therefore, 3.5 boys can finish the job in 1×1563.5= 47 days.


 


 

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Q:

9 girls working 7 hours a day can complete a piece of work in 15 day. In how many days can 6 girls working for 9 hours a day, complete the same piece of work?

A) 35/4 days B) 17.5 days
C) 19 3/4 days D) 37/3 days
 
Answer & Explanation Answer: B) 17.5 days

Explanation:

Let the number of days be 'p' 

As the work is same, we know that

M1 x D1 x H1 = M2 x D2 x H2

Where M = Men, D = Days, H = Hours per day 

Here M1 = 9, D1 = 15, H1 = 7 

M2 = 6, D2 = p, H2 = 9 

=> 9 x 15 x 7 = 6 x p x 9 

=> p = 35/2 = 17.5 days.

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Q:

Aadi can do a piece of work in 12 days alone, Bunny can do the same work in 16 days alone. After Aadi has been working for 5 days and Bunny for 7 days, Charan finishes it in 14 days. In how many days will Charan alone be able to do the work?

A) 96 days B) 48 days
C) 24 days D) 12 days
 
Answer & Explanation Answer: A) 96 days

Explanation:

Let number of days Charan can do the same work alone is 'd' days.

According to the given data,

512 + 716 + 14d = 114d = 1 - 20 + 214814d = 48 - 4148d = 14 x 487d = 96 days

 

Therefore, Charan alone can complete the work in 96 days.

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Q:

A,B,C can complete a work in 15,20 and 30 respectively.They all work together for two days then A leave the work,B and C work some days and B leaves 2 days before completion of that work.how many days required to complete the whole work?

Answer

Given A,B,C can complete a work in 15,20 and 30 respectively.


The total work is given by the LCM of 15, 20, 30 i.e, 60.


A's 1 day work = 60/15 = 4 units


B's 1 day work = 60/20 = 3 units


C's 1 day work = 60/30 = 2 units


(A + B + C) worked for 2 days = (4 + 3 + 2) 2 = 18 units


 Let B + C worked for x days = (3 + 2) x = 5x units


C worked for 2 days = 2 x 2 = 4 units


Then, 18 + 5x + 4 = 60


22 + 5x = 60


5x = 38


x = 7.6


 


Therefore, total number of days taken to complete the work = 2 + 7.6 + 2 = 11.6 = 11 3/5 days.

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