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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:

Three athletes can complete one round around a circular field in 16, 24 and 36 min respectively. They start running together at same instant then after how much time they will meet to each other for first time ?

A) 2 hrs 24 min B) 2 hrs 44 min
C) 1 hrs 24 min D) 1 hrs 24 min
 
Answer & Explanation Answer: A) 2 hrs 24 min

Explanation:

Given that three athletes can complete one round around a circular field in 16, 24 and 36 min respectively.

Now, required time after which they met for the first time = LCM of (16, 24 & 36) min

Now, LCM of 16, 24, 36 = 144 minutes = 2 hrs 24 min.

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Q:

K can finish the work in 18 days and L can do the same work in 15 days. L worked for 10 days and left the job. In how many days, K alone can finish the remaining work ?

A) 5.5 days B) 6 days
C) 4.2 days D) 5 days
 
Answer & Explanation Answer: B) 6 days

Explanation:

L's 10 days work = 115×10=23

 


Remaining work = 1-23=13

 


Now,  work is done by K in one day = 1/18

 

1/3 work is done by K in  18×13 = 6 days

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Q:

A can complete a work in 12 days with a working of 8 hours per day. B can complete the same work in 8 days when working 10 hours a day. If A and B work together, working 8 hours a day, the work can be completed in --- days  ?

A) 51/24 B) 87/5
C) 57/12 D) 60/11
 
Answer & Explanation Answer: D) 60/11

Explanation:

A can complete the work in 12 days working 8 hours a day

=> Number of hours A can complete the work = 12×8 = 96 hours 

=> Work done by A in 1 hour = 1/96

 

B can complete the work in 8 days working 10 hours a day

=> Number of hours B can complete the work = 8×10 = 80 hours 

=> Work done by B in 1 hour = 1/80

 

Work done by A and B in 1 hour = 1/96 + 1/80 = 11/480

 => A and B can complete the work in 480/11 hours

 

A and B works 8 hours a day.

Hence total days to complete the work with A and B working together 

= (480/11)/ (8) = 60/11 days

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4 4349
Q:

K, L and M can do a piece of work in 20, 30 and 60 days respectively. In how many days can K do the total work if he is assisted by L and M on every third day ?

A) 15 days B) 13 days
C) 12 days D) 10 days
 
Answer & Explanation Answer: A) 15 days

Explanation:

In one day work done by K = 1/20

Work done by K in 2 days = 1/10

 

Work done by K,L,M on 3rd day =1/20 + 1/30 + 1/60 = 1/10

Therefore, workdone in 3 days is = 1/10 + 1/10 = 1/5

 

1/5th of the work will be completed at the end of 3 days.

The remaining work = 1 - 1/5 = 4/5

1/5 of work is completed in 3 days

Total work wiil be done in 3 x 5 = 15 days.

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3 4245
Q:

There is sufficient salary to give K for 10 days and L for 15 days. Then how many days will the money last if both has to be given the salary ?

A) 6 days B) 12 days
C) 4 days D) 9 days
 
Answer & Explanation Answer: A) 6 days

Explanation:

K's 1 day's salary = 1/10
L's 1 day's salary = 1/15
Together their 1 day's salary = 1/10 + 1/15
= 3/30 + 2/30
= 5/30
= 1/6
So the money will be enough for paying them both for 6 days.

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3 4223
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 4223
Q:

A alone can do a work in 20 days. B is 125% more efficient than A. A and B started working and worked for 4 days. If C alone completed the remaining job in 22 days. How many days C alone takes to complete the entire job?

A) 30 B) 35
C) 40 D) 42
 
Answer & Explanation Answer: C) 40

Explanation:
A alone can do = 20days 
 
Efficiency ratio of A & B= 4 : 5

Time required will be in ratio = 5:4

B alone will do it in =16 days

LCM of (16,20)= 80 ,
 
Assume work size of 80 units

 

1 day work of A= 4 units 1 day work of B= 5 units

 

Work done by both in 4 days= 4*(5+4)= 36 units

 

Work left= 80-36= 44 units

 

Now C takes 22 days to complete= 44 units.

 

Time taken by C alone to complete the work= 40 days
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Q:

One girl can eat 112 chocolates in half a minute, and her boy friend can eat half as many in twice the length of time. How many chocolates can both boy and girl eat in 12 seconds ?

A) 44 B) 32
C) 56 D) 49
 
Answer & Explanation Answer: C) 56

Explanation:

Girl eats 112 chocolates in 30 sec

so she can eat in 12 sec is 12 x 112/30 = 44.8 chocolates.

 

Her boy friend can eat one-half of 112 in twice of 30 sec

so he can eat 56 in 60 sec


Then he can eat in 12 sec is 56 x 12/60 = 11.2 chocolates.

 

Hence, together they can eat = 44.8 + 11.2 =56 chocolates in 12 seconds.

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