Proportionally, the unit price is fixed, and the material weight is directly proportional to the total price. Formula:

Material weight: total price = material weight: total price

2000: 900=X:500

900X= 1000000

X= 1000000÷900

x≈ 1 1 1 1. 1 1

So 500 yuan is111.1/kg.

or

Find the unit price first: unit price = total price ÷ weight =900÷2000=9/20 (yuan)

Find the weight again: weight = total price ÷ unit price = 500 ÷ 9/20 = 500× 20/9 =10000 ÷ 9 ≈11.