MarketGeometry, you asked how that number (54) was calculated. Is that not so?
The answer was provided as it has been given on this board with that formula and original source data.
It is correct in that it is the manner in which it was calculated. Check the DD if you are unsure how it was made.
Is the number correct in the sense of being the correct answer to the question "What is the book value per common share?" No it is not.
You are correct that preferred equity amounts (Senior and Junior Preferred) must be subtracted from the Total Shareholder Equity before dividing by outstanding common shares.
The standard formula for calculating BVPCS when there are preferred shares is:
Book Value Per Share = Total Shareholder's Equity - Preferred Equity Average Outstanding Common Stock
Now since you already knew this and were ready to mount a correction then let us see where you are in that.
Here is Fannie Mae stockholders’ equity: Senior preferred stock, 1,000,000 shares issued and outstanding - $117,149,000,000 Preferred stock, 700,000,000 shares are authorized—555,374,922 shares issued and outstanding, respectively - $19,130,000,000 Common stock, no par value, no maximum authorization—1,308,762,703 shares issued, respectively, 1,158,077,970 shares outstanding, respectively. - $687,000,000 Accumulated deficit - ($68,276,000,000) Accumulated other comprehensive income - $1,038,000,000 Treasury stock, at cost, 150,684,733 shares, respectively - ($7,401,000,000) Total Fannie Mae stockholders’ equity - $62,327,000,000