NTPC's stake sale may help raise about Rs 50 billion ($729 million) after investors bid for more than double the 5 percent stake offered in the country's biggest power generator. Investors subscribed to 843.3 million shares, compared to 412.3 million on sale at a floor price of 122 rupees apiece at the end of the second and final day of the sale, according to stock exchange data. Retail investors bid for 44 percent of their quota on Wednesday with the balance being bought by institutional buyers. The government had reserved 20 percent of the shares for retail buyers.