In a small dairy farm, 40 cows eat 20 bags of grass in 40 days. In how many days one cow will eat one bag of grass?
Choose the correct answer
A) 40 B) 80 C) 60 D) 50 E) 90
Assume that in a days, one cow will eat one bag of grass.   More cows, less days (Indirect proportion)   More bags, more days (direct proportion)   Hence we can write as (cows)40:1   ::x:40   (bags)1:20   ⇒40×1×40=1×20×x   ⇒x=80   ANSWER:80
<result>B</result>
In a small dairy farm, 40 cows eat 20 bags of grass in 40 days. In how many days one cow will eat one bag of grass?