Time and Work 1/2

7.  A is thrice as good a work man as B and takes 10 days less to do a piece of work than B takes. B can do the work in :
a. 12 days
b. 15 days
c. 20 days
d. 30 days

8.  A can complete a job in 9 days B in 10 days and C in 15 days. B and C start the work and are forced to leave after 2 days. The time taken to complete the remaining work is :
a. 6 days
b. 9 days
c. 10 days
d. 13 days

9.  A completes a work in 6 days, B works $1\displaystyle\frac{1}{2}$ times as fast as A. How many days it will take for A and B together to complete the work ?
a. $4\displaystyle\frac{7}{{12}}$
b. $3\displaystyle\frac{5}{{12}}$
c. $4\displaystyle\frac{4}{5}$
d. None of these

10.  Twelve men can complete a work in 8 days. Three days after they started the work, 3 more men joined them. In how many days will all of them together complete the remaining work ?
a. 2
b. 4
c. 5
d. 6

11.  A and B can complete a work in 10 days and 15 days respectively. B starts the work and after 5 days A also joins him. In all, the work would be completed in :
a. 7 days
b. 9 days
c. 11days
d. None of these

12.  A can do a piece of work in 80 days. He works at it for 10 days and then B alone finishes the work in 42 days. The two together could complete the work in :
a. 24 days
b. 25 days
c. 30 days
d. 35 days