DMM Corporation is a diversified U.S. firm that has ownership stakes in two other U.S. corporations. Specifically, DMM Corporation owns 60% of the outstanding stock of Tax Shelter.com and 10% of the outstanding stock of Litigation.com. During the year 2013, DMM Corporation itself had $10 million of taxable income; TaxShelter.com and Litigation.com had $2 million and $3 million net operating losses, respectively. Neither TaxShelter.com nor Litigation.com has ever reported positive taxable income, and neither pays any dividends.

a. What percentage of stock ownership is required for tax consolidation?