A, B, C and D can do a piece of work in 40 days. If A and B can do it together in 100 days,
and C alone in 120 days, find the time in which D alone can do it.

A and B can do a piece of work in 6 days and C in 12 days. In how many days will A, B and
C do it together?

A can do a piece of work in 40 days. He worked at it for 5 days then B finished it in 21
days. In how many days can A and B together finish the work?

12 men can dig a trench in 36 days working 10 hrs/day. How many hours a day of daily
work will be required of 36 men working for 30 days to dig that trench?

20 men, 30 women and 60 children working 6 hours/day build a 200 m long 2 m high and
40 cm wide wall in 20 days. How long a wall 1.5 m high and 60 cm wide will 30 men, 15 women
and 30 children build, working 9 hours/day in 15 days?