Let true cost price for 1 kg = 1000 g
He sells at cost price but makes 20% profit using false weight, meaning:
Let actual weight given = (x) grams
He charges for 1000 g but gives only (x) g.
Profit condition:
Profit %=x1000−x×100=20
Solve:
x1000−x=0.2
1000 - x = 0.2x
1000 = 1.2x
x=1.21000=833.33
Final Answer: 833.33 grams