7.  A can do a piece of work in 4 hours; B and C together can do it in 3 hours, while A and C together can do it in 2 hours. How long will B alone take to do it?  
Answer: Option C Explanation:
B alone will take 12 hours to do the work. 
8.  A can do a certain work in the same time in which B and C together can do it. If A and B together could do it in 10 days and C alone in 50 days, then B alone could do it in:  
Answer: Option C Explanation:
A’s 1 day’s work = (B + C)’s 1 day’s work …. (ii)
So, B alone could do the work in 25 days. 
9.  A does 80% of a work in 20 days. He then calls in B and they together finish the remaining work in 3 days. How long B alone would take to do the whole work?  
Answer: Option C Explanation:
Whole work will be done by A and B in (3 x 5) = 15 days.

10.  A machine P can print one lakh books in 8 hours, machine Q can print the same number of books in 10 hours while machine R can print them in 12 hours. All the machines are started at 9 A.M. while machine P is closed at 11 A.M. and the remaining two machines complete work. Approximately at what time will the work (to print one lakh books) be finished ?  
Answer: Option D Explanation:
So, the work will be finished approximately 2 hours after 11 A.M., i.e., around 1 P.M. 