P can do a piece of work in 20 days, Q can do the same

Solution

P – 20 days                                                          P – 6 unit Q – 24 days                      LCM = 120                Q – 5 unit R – 30 days                                                          R – 4 unit Work of all 3 per day is (6 + 5 + 4) – 15 units All worked for 4 days. So, 4 days work is 4 × 15 = 60 units Remaining work = 120 – 60 = 60 units That work done by Q and R their per day unit = (5 + 4) = 9 unit Remaining work done by Q and R is 60/9 days = 6(2/3) days