17.  A is 30% more efficient than B. How much time will they, working together, take to complete a job which A alone could have done in 23 days?  
Answer: Option B Explanation:
Ratio of times taken by A and B = 100 : 130 = 10 : 13. Suppose B takes x days to do the work.
Therefore, A and B together can complete the work in 13 days. 
18.  Ravi and Kumar are working on an assignment. Ravi takes 6 hours to type 32 pages on a computer, while Kumar takes 5 hours to type 40 pages. How much time will they take, working together on two different computers to type an assignment of 110 pages?  
Answer: Option C Explanation:

19.  A, B and C can complete a piece of work in 24, 6 and 12 days respectively. Working together, they will complete the same work in:  
Answer: Option C Explanation:

20.  Sakshi can do a piece of work in 20 days. Tanya is 25% more efficient than Sakshi. The number of days taken by Tanya to do the same piece of work is:  
Answer: Option B Explanation:
Ratio of times taken by Sakshi and Tanya = 125 : 100 = 5 : 4. Suppose Tanya takes x days to do the work.
x = 16 days. Hence, Tanya takes 16 days to complete the work. 