If 15 men, working 9 hours a day, can reap a field in 16 days, in how many days will 18 men reap the field, working 8 hours a day?  Pick one:
A) 10 B) 15 C) 20 D) 25 E) None of them
Let the required number of days be x.   More men, Less days (indirect proportion)   Less hours per day, More days (indirect proportion)   Men 18 : 15   Hours per day 8: 9 } : :16 : x   (18 x 8 x x)=(15 x 9 x 16)= x=(44 x 15)144 = 15   Hence, required number of days = 15.   Answer is 15.
<result>B</result>
If 15 men, working 9 hours a day, can reap a field in 16 days, in how many days will 18 men reap the field, working 8 hours a day?