Ganga and Saraswati, working separately can plough a field in 8 and 12 hours respectively. If they work in stretches of one hour alternately. Ganga begins at 9 a.m., when will the ploughing be completed ?

Explanation:

According to question,

Ganga begins at 9 am and she does 3 units / hours Saraswati begins at 10 am an she does 2 units/hours

So by 11 am they complete 5 units

time =T.W\ (3+2)=24\5=(4 cycle of 2 hrs each + 4 units left)

and Now Ganga will complete 3 unit out of 4 units in 1 hr

Now, Rest 1 unit work done by

=1\2hr

Total time=8+1+ 1\2=9 1\2hr

Hence,

work finished at =9 am+9 1\2hr=6:30 Pm