Question: 31 -

 Daniel can do some work in 12 hours, Roy can do the same work in 10 hours while Hillari can do the same work in 15 hours. All the three of them start working at 9 a.m while Daniel stops works at 11 a.m and remaining two complete the work. Approximately at what time will the work be finished?

12.30 am

2.00 pm

1.30 pm

1.00 pm

Answer:

2.00 pm

Solution:

Daniel= 12 hrs so 1 hr work = 1/12 
Similarly Roy= 1/10 and Hillari =1/15
In 1 hr they will do 1/12+1/10+1/15= 1/2 in 1 hr 
so in 2 hrs (9 am -11 am) work done is 1/2 
Now Daniel stops working so Roy and Hillari work together 
1/10+1/15 = 1/6 in 1 hr
So 1 in 6 hr hence 1/2 in 3 hr hence three hours from 11 am 
they will finish the work that is 2pm.