Q21. 
A man can do a piece of work in 60 hours. If he takes his son with him and both work together then the work is finished in 40 hours. How many hours will the son take to do the same job, if he worked alone on the job? 
A.  20 

B.  60 

C.  100 

D.  120 
Q22. 
Aditya, Vedus and Yuvraj alone can do a job for 6 weeks, 9 weeks and 12 weeks respectively. They work together for 2 weeks. Then, Aditya leaves the job. Vedus leaves the job a week earlier to the completion of the work. The job would be completed in: 
A.  4 weeks 

B.  5 weeks 

C.  7 weeks 

D.  None of these 
Q23. 
Due to hole at the bottom of the tank, a tap takes 2 more minutes to completely fill the tank. Due to leakage of water through this hole, a bucket filled completely with water gets emptied in 4 minutes. In how much time can the tap fill the tank, if there was no hole at the bottom at the tank? 
A.  8 min 

B.  2 min 

C.  4 min 

D.  6 min 
Q24. 
$A$ can complete a project in 20 days and $B$ can complete the same project in 30 days. If $A$ and $B$ start working on the project together and $A$ quits 10 days before the project is completed, in how many days will the project be completed? 
A.  18 

B.  27 

C.  26.67 

D.  16 
Q25. 
A red light flashes 3 times per minute and a green light flashes 5 times in two minutes at regular intervals. If both lights start flashing at the same time, how many times do they flash together in each hour? 
A.  30 

B.  29 

C.  31 

D.  32 