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?	Pick
A) 9
B) 12
C) 10
D) 13
E) 15
Explanation:   Let the required number of days be x   More persons, less days (indirect proportion)   More hours, less days (indirect proportion)   Hence we can write as   (persons)39:30   (hours) 5:6}:: x:12   ⇒39×5×12=30 × 6 × x   ⇒39×5×2=30 × x   ⇒39=3×x   ⇒x=13   Answer: Option 13
<result>D</result>
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?