A can do a piece of work in 20 days and B in 40 days. A begins the work and there after A and B work on alternate days, the work then finishes during the course of the ________ day when ___________ is working.
- 26th Day, A
- 27th Day, A
- 25th Day, B
- 29th Day, B
- 27th Day, B
The Usual Method
Amount of work A finishes in 1 day = ,
Similarly, amount of work B finishes in 1 day =
Thus the amount of work finished in two consecutive days =
Hence total number of days needed to finish the work:
in 2 days means in 1 day.
Thus it will be the 27th day on which the work will finish.
As can be seen, that since A started to work on the 1st day and B on the 2nd day and so on alternately, A will be working on all odd numbered days and B on all even numbered days. Thus on the 27th Day, A will be working.
Estimated Time to arrive at the answer = 60 seconds.
Since, A works on the 1st day and B on the 2nd and so on alternately, A will be working only on odd numbered days. Thus, option ‘1’ can be eliminated since A cannot work on the 26th day. Similarly, options ‘3’, ‘4’ and ‘5’ can also be eliminated since B works only on even numbered days. This leaves us only with the options ‘2’.
Estimated Time to arrive at the answer = 5 seconds.