Answers

2016-01-13T13:03:32+05:30
560 persons   -----------9 months
 ?                    -----------7 months

they are in inverse proportion
so
560 x 9 / 7 =720
therefore 
no. of persons required to complete work in 7 months  = 720 persons
2 5 2
2016-01-13T13:10:24+05:30
560 x 9 / 7 =720
therefore 
no. of persons required to complete work in 7 months  = 720 persons
1 5 1