Final answer:
The number of shares used in computing basic and diluted earnings per share for the year ended December 31, 2011 is 2,250,000 shares.
Step-by-step explanation:
The number of shares to be used in computing basic earnings per share for the year ended December 31, 2011 is calculated by adding the shares outstanding at the beginning of the year (1,800,000 shares) to the shares issued during the year (150,000 shares + 300,000 shares), resulting in a total of 2,250,000 shares.
The diluted earnings per share takes into account the convertible bonds. Since no bonds were converted into common stock in 2011, the number of shares used for diluted earnings per share is the same as the basic earnings per share, which is 2,250,000 shares.