GRE 17- A shopkeeper sells his goods using 20% lesser weight and professes to sell the goods...

A shopkeeper sells his goods using 20% lesser weight and professes to sell the goods at the cost price. How much does he gain from his lie? Indicate the correct option. A shopkeeper sells his goods using 20% lesser weight and professes to sell the goods at the cost price. How much does he gain from his lie? Indicate the correct option.
A)5%
B)8%
C)20%
D)25%
E)10%

Correct Answer: D
Explanation: Let his cost price be $100 per kg Selling price for 1 kg-20% of 1 kg = $100
Selling price for 1-0.2*1=0.8 kg is $100
Cost price per gram = 100/1000 = 1/10
Selling price per gram = 100/800 = 1/8
Profit %= (Selling price-cost price)/Cost price*100
= (1/8-1/10)/(1/10)*100
= (10-8)/80*1000
= 2/80*1000
= 25% Option D is true.