A shopkeeper claims to sell 450 kg rice at a cost price of ₹40 per kg but uses a weight of 900 grams instead of a one kilogram weight. He makes a profit of ₹2,520 by selling the remaining rice in the black market. The ratio of the black-market price to the original price per kg of rice is:
1
7 : 5
2
10 : 7
3
9 : 4
4
4 : 3