How much do 20 pencil cost if 4 pencils cost rupees three?
To help you understand this question, we will create a new
temporary word. We will call every 4 pencils a "pencilor". So a
"pencilor" cost 3 rupees.
How many "pencilor" is there in 20 pencils? Well, 20 = 4 x 5,
meaning there are 5 groups of 4 => there are 5 "pencilors". If
each "pencilor" cost 3 rupees, how much does 5 cost? 3 x 5 = 15
rupees. And you are done.