Question

if 25 pencils cost rupees 112.50 , what will be the cost of 18 pencils

Answer 1

Cost of 25 pencils=Rs. 112.50
Cost of 1 pencil=112.5/25=4.5

cost of 18 pencils =18×4.5=81

So the cost of 18 pencils is 81 rupees.

Answer 2

let
x1 be 25
y1 be 112.5
x2 be 18
then y2 be ?
so we have
x1/y1=x2/y2
25/112.5=18/x
x=112.5/25*18
= 81