A dishonest dealer professes to sell his goods at the cost price but uses a weight of 900 gm for one kg weight. Find his gain percent.

$11 \frac{1}{9}$%

Percentage gain = \(\frac{( SP - CP ) }{CP}\) × 100%

   Cost price   :    Selling price

     900          :       1000

Percentage gain = \(\frac{( 1000 - 900 ) }{900}\) × 100%

= \(\frac{( 100 ) }{900}\) × 100%

= 11\(\frac{( 1) }{9}\)%

The correct answer is Option (3) → $11 \frac{1}{9}$%