21. P can complete work in 12 days working 8 hrs a day. Q can complete the same work in 8 days working10 hrs a day. If both P and Q working 8 hrs a day in how many days can they complete the work? 


22. A and B can do a piece of work in 72 days; B and C can do it in 120 days; A and C can do it in 90 days In what time can A alone do it? 


23. A and B can do a piece of work in 5 days; B and C can do it in 7 days and A and C can do it in 4 days who among these will take least time if put to do it alone? 


24. A can do a piece of work in 4hrs.B and C together can do it 3 hrs while A and C can do it in 2 hrs how long it will take for B? 


25. A can do piece of work in 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? 


26. A is thrice good a workman as B and therefore is able to finish a job in 60 days less than B. Working together they can do it in? 


27. 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? 


28. A can do a work in 15 days and B in 20 days. If they work on it together for 4 days then the fraction of the work that is left is? 


29. X can do a piece of work in 40 days. He works at it for 8 days and then Y finished it in 16 days how long will they work together take to complete the work? 


30. A alone can complete a work in 16 days and B alone can complete in 12 days. Starting with A they work on alternate days. The total work will be completed in? 


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Those are all planning for any competitive examinations can use this segment to enhance their abilities.