A balance of a trader weighs 10% less then it should be. still the trader marks-up his goods to get the overall profit of 20%. What is the mark up on the cost price?

Let the CP be Rs. 1 per g
but he weighs 900 g for every 1000 g
∴ value of goods sold = 900
Now, let the markup be x%
∴ MP = 1000 + 1000x / 100 = ( 1000 + 10x )
but since MP = SP,
∴ SP = ( 1000 + 10x )
Hence, profit (%) = [{( 1000 + 10x ) - 900} / 900] x 100 = 20
⇒ x = 8
Thus the markup = 8%