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A, B and C can do a piece of work in 20, 30 and 60 days respectively
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08 Jul 2020, 13:02
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A, B and C can do a piece of work in 20, 30 and 60 days respectively. In how many days can A do the work if he is assisted by B and C on every third day?
A. 12 days
B. 15 days
C. 16 days
D. 18 days
E. 19 days
A. 12 days
B. 15 days
C. 16 days
D. 18 days
E. 19 days
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Re: A, B and C can do a piece of work in 20, 30 and 60 days respectively
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08 Jul 2020, 22:47
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Amount of work done by A in 1 day = 1/20th of the work
Therefore work done by A every 3 days = 3 * 1/20 = 3/20
Amount of work done by B and C in 1 day(i.e on the third day) = (1/30 + 1/60) = 1/20th of the work
Work done by A + B + C every 3 days = (3/20 + 1/20) = 1/5 th of the work
Therefore they will have to do 1/5th of the work 5 times to complete the work (1/5 + 1/5 + 1/5 + 1/5 + 1/5) and each 1/5 th of the work takes 3 days
Therefore Total Time= 5 * 3 = 15 days
Option B
Arun Kumar
__________________________
Key Notes
(1) Completion of work is = 1. Any incomplete work is a fraction.
(2) To find the time taken when 2 or more people/machines work together, we do not add the individual time.
Instead we convert time taken into work/unit time and then add the work that is done.
eg if A can do a piece of work in 5 days, in 1 day he can do 1/5th of the work.
if B can do the same piece of work in 10 days, in 1 day he can do 1/10th of the work.
Therefore the total work don in 1 day = 1/5 + 1/10 = 3/10th of the work in 1 day.
To find the number of days, flip the numerator and denominator, and we get 10/3 days.
Therefore work done by A every 3 days = 3 * 1/20 = 3/20
Amount of work done by B and C in 1 day(i.e on the third day) = (1/30 + 1/60) = 1/20th of the work
Work done by A + B + C every 3 days = (3/20 + 1/20) = 1/5 th of the work
Therefore they will have to do 1/5th of the work 5 times to complete the work (1/5 + 1/5 + 1/5 + 1/5 + 1/5) and each 1/5 th of the work takes 3 days
Therefore Total Time= 5 * 3 = 15 days
Option B
Arun Kumar
__________________________
Key Notes
(1) Completion of work is = 1. Any incomplete work is a fraction.
(2) To find the time taken when 2 or more people/machines work together, we do not add the individual time.
Instead we convert time taken into work/unit time and then add the work that is done.
eg if A can do a piece of work in 5 days, in 1 day he can do 1/5th of the work.
if B can do the same piece of work in 10 days, in 1 day he can do 1/10th of the work.
Therefore the total work don in 1 day = 1/5 + 1/10 = 3/10th of the work in 1 day.
To find the number of days, flip the numerator and denominator, and we get 10/3 days.
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A, B and C can do a piece of work in 20, 30 and 60 days respectively
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09 Jul 2020, 12:06
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Taking the LCM Method.
By taking LCM and assuming that LCM to be total work.
Which in this case will be LCM(20, 30,60) -->60 Units
In 20 days A can do 60Units of work
Means in 1 day he will do 3 Units
Similarly,
In 30 days B can do 60Units of work
Means in 1 day he will do 2 Units
And,
In 60 days C can do 60Units of work
Means in 1 day he will do 1 Unit
From the above info in every three days work done is 3+3+3+2+1 = 12 Units
Total work which needs to be done is 60
So total days will be (60/12)*3 =15
Answer is B
Posted from my mobile device
By taking LCM and assuming that LCM to be total work.
Which in this case will be LCM(20, 30,60) -->60 Units
In 20 days A can do 60Units of work
Means in 1 day he will do 3 Units
Similarly,
In 30 days B can do 60Units of work
Means in 1 day he will do 2 Units
And,
In 60 days C can do 60Units of work
Means in 1 day he will do 1 Unit
From the above info in every three days work done is 3+3+3+2+1 = 12 Units
Total work which needs to be done is 60
So total days will be (60/12)*3 =15
Answer is B
Posted from my mobile device