GMATDemiGod wrote:
elch4ngo wrote:
narmit wrote:
My approach is slightly different:
John+Jane can complete the work in 7.5 days (20*12)/(20+12).
Jane left 4 days before the work got completed...that means they together worked for 3.5 days.
Now with rate of 1/20 and 1/12 per day..combined...they can do...2/15 work in 1 day. That means in 3.5 days, then can do -->7/15 of work.
So left over work is 8/15 and needs to be be done by John alone.
which would take him...(1/20)/(8/15)--->32/3 days...
This is taking me nowhere..Can anyone suggest what is wrong in this logic??
i did exactly the same and got stucked too... (just note the following in your last calc. -> (1/20)/(8/15) = 36/3 = 12 days
not sure what is wrong, i learned this approach from manhattan and usually works fine
Having the same issue as both of these people with this method.
I think this method, because it seems straight forward in my brain, but this is the second time ive been hung up on a question. And got the answer by choosing the closest answer. But something is off logic wise.
Can Bunuel or Engr2012 help if possible
?
There is a problem in this logic.
"Jane was indisposed 4 days before the work got over." - implies that Jane left 4 days before the work actually got over. So perhaps only 1 day work was left but Jane left and John alone completed the work in 4 days. After Jane left, the work continued for 4 days.
In your logic, John and Jane would have taken total 7.5 days and Jane left after 3.5 days. But then, the leftover work would have been completed in more than 4 days because John was working alone.
In such questions, you need to start from the end. Last 4 days John works alone and completes 4 * (1/20) = 1/5 of the work.
So 4/5 of the work should have been completed by the two of them together before Jane left.
Their combined rate of work is 1/20 + 1/12 = 8/60
Time taken to complete 4/5 of the work = (4/5)/(8/60) = 6 days.
So total number of days taken to complete the work = 6 + 4 = 10 days.
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