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15 Aug 2017, 23:30
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Hello BrushMyQuant, abhimahna, and Bunuel
If we are given that A can do a work in 12 hours and B can do the same work in 18 hours. A started the work and B joined him after 6 hours. How much time will they both take to complete the work?
Let total work = 36
A can do 3 units per hour
B can do 2 units per hour
Together they finish 5 units per hour
A started the work and worked alone for 6 hours. Therefore A finished 18 units of work.
Amount of work left= 36-18= 18
I am confused about the steps from here.
What I dis was, I found new units per hour for both A and B
A= 3/2 UNITS/HOUR
B= 1 UNIT/HOUR
AND got the answer 36/5 which is incorrect.
What is the error in the above method?
If we are given that A can do a work in 12 hours and B can do the same work in 18 hours. A started the work and B joined him after 6 hours. How much time will they both take to complete the work?
Let total work = 36
A can do 3 units per hour
B can do 2 units per hour
Together they finish 5 units per hour
A started the work and worked alone for 6 hours. Therefore A finished 18 units of work.
Amount of work left= 36-18= 18
I am confused about the steps from here.
What I dis was, I found new units per hour for both A and B
A= 3/2 UNITS/HOUR
B= 1 UNIT/HOUR
AND got the answer 36/5 which is incorrect.
What is the error in the above method?
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15 Aug 2017, 23:42
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Shiv2016
Hi Shiv2016 ,
The steps highlighted above are incorrect.
Why are you calculating the new unit of work? I mean you cannot say that the efficiency of A and B would change when the work left is less.
As per your method, you found that both A and B are doing the work at 5 units/hour.
Work left when B joined = 18 units.
If they are doing at the rate of 5 units per hour, total time taken to complete the whole work = 18/5 = 3 hours and 36 mins.
Does that make sense?
16 Aug 2017, 00:03
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abhimahna
abhimahna thank you for your reply.
When we find their efficiency for completing the work, we find it according to the amount of work given. Won't it change when the amount of work will change?
