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 Time and Work Questions

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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 : 

Efficiency∝1No 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:

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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2 4381
Q:

A shopkeeper has a job to print certain number of documents and there are three machines P, Q and R for this job. P can complete the job in 3 days, Q can complete the job in 4 days and R can complete the job in 6 days. How many days the shopkeeper will it take to complete the job if all the machines are used simultaneously ?

A) 4/3 days B) 2 days
C) 3/2 days D) 4 days
 
Answer & Explanation Answer: A) 4/3 days

Explanation:

Let the total number of documents to be printed be 12.

 The number of documents printed by P in 1 day = 4.

 The number of documents printed by Q in 1 day = 3.

 The number of documents printed by R in 1 day = 2.

 
Thus, the total number of documents that can be printed by all the machines working simultaneously in a single day = 9.

 

Therefore, the number of days taken to complete the whole work = 12/9 = 4/3 days.

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4 4335
Q:

A is 1.5 times efficient than B therefore takes 8 days less than B to complete a work. If A and B work on alternate days and A works on first day, then in how many days the work will be completed?

A) 17 B) 19
C) 19.5 D) 21
 
Answer & Explanation Answer: B) 19

Explanation:
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2 4314
Q:

A can complete 9/10 part of a work in 31 days. After that, with the help of B he can complete the remaining work in 4 days. In how many days will  A and B together can complete that work ?

A) 36 B) 40
C) 42 D) 38
 
Answer & Explanation Answer: B) 40

Explanation:

Remaining work = 1 - 9/10 = 1/10

 

=> A & B together completes 1/10 of work in 4 days

 

=> 1 work can completed in ------ ? days

 

Let it be x days

 

=>  4110=x1

 

=> x = 40 days.

 

Hence, A & B together can complete the work in 40 days.

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11 4284
Q:

A town having teenagers(boys & girls) of 5000 requires 150 litre of water per head. It has a tank measuring 20 m × 15 m × 5 m. The water of this tank will sufficient for ____ days.

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

Explanation:

Total Water reqduired = 5000 × 150 lit = 750,000 litres = 750 cu.m.

 

Volume of tank = 20 × 15 × 5 = 1500 Cu.m.

 

Number of days required =1500/750 = 2 days.

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6 4233
Q:

12 men complete a work in 14 days. 5 days after they had started working, 3 men join them. How many more days will all of them take to complete the remaining work?

A) 5 B) 4
C) 3 D) 2
 
Answer & Explanation Answer: C) 3

Explanation:

Let p be the required number of days.

From the given data,

12 x 14 = 12 x 5 + (12+3) x p 

12 x 14 = 12[5 + 3p]

14 = 5 + 3p

3p = 9

p = 3 days.

 

Hence, more 3 days all of them take to complete the remaining work.

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2 4189
Q:

A, B and C together can finish a task in 12 days. A is twice as productive as B and C alone can do the task in 36 days. In how many days can A and B do the task if C goes on leave?

A) 10 B) 20
C) 15 D) 18
 
Answer & Explanation Answer: D) 18

Explanation:
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Q:

Tushar takes 6 hours to complete a piece of work, while Amar completes the same work in 10 hours. If both of them work together, then what is the time required to complete the work?

 

A)  3 hours B) 3 hours 15 minutes
C) 3 hours 30 minutes D) 3 hours 45 minutes
 
Answer & Explanation Answer: D) 3 hours 45 minutes

Explanation:

Let them take x hours working together

1/x = 1/10 + 1/6 = 8/30

X= 30/8 hours = 15/4 hours = 3 hours 45 minutes

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