39 persons can repair a road in 12 days , working 10 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 : 10 30 x 6 x x = 39 x 10 x 12 x = ( 39 x 10 x 12 ) / ( 30 x 6 ) x = 26 . answer : e"
divide(multiply(multiply(39, 12), 10), multiply(30, 6))