39 persons can repair a road in 12 days, working 5 hours a day. In how many days will 30 persons, working 6 hours a day, complete the work?

Let the required number of days be x.

Less persons, More days (Indirect Proportion)

More working hours per day, Less days (Indirect Proportion)

Persons	30	:	39		:: 12 : x
Working hours/day	6	:	5

 30 x 6 x x = 39 x 5 x 12

x =	(39 x 5 x 12)
	(30 x 6)

 x = 13.