Q16. 
A can build up a structure in 8 days and B can break it is 3 days. A has worked for 4 days and then B joined to work with A for another 2 days only. In how many days will A alone build up the remaining part of the structure? 
A.  10 

B.  9 

C.  12 

D.  None 
Q17. 
Two workers $A$ and $B$ manufactured a batch of identical parts. $A$ worked for 2 hours and $B$ worked for 5 hours and they completed half the job. Then they worked together for another 3 hours and they had to do (1/20)th of the job. How many hours time does $B$ take to complete the job, if he worked alone? 
A.  24 

B.  12 

C.  15 

D.  30 
Q18. 
$A$ and $B$ borrowed a tractor for 23 days. $A$ ploughed 12 acres per day for a certain number of days and then Bused it to plough 15 acres per day for the remaining days. If they paid Rs 3,000 and Rs 2,000 respectively, for how many days did $A$ use the tractor? 
A.  12 

B.  15 

C.  16 

D.  18 
Q19. 
$A$, $B$ and $C$, can complete a piece of work individually in 15, 30 and 40 days respectively. They started the work together and the $A$ and $B$ let 2 days and 4 days before the completion of the work respectively. In how many days was the work completed? 
A.  $10\dfrac{13}{15}$ 

B.  $12$ 

C.  $15$ 

D.  $10\dfrac{2}{15}$ 
Q20. 
Pipes $A$ and $B$ can fill a tank in 12 min and 16 min respectively. Both are kept open for '$n$' min and then $B$ is closed and $A$ fills the rest of the tank in 5 min. The time '$n$' after which $B$ was closed is: 
A.  3 min 

B.  2 min 

C.  5 min 

D.  4 min 