Pentex and Marbro, small companies in the stationery business, each had a dollar gross margin of $20,000 during September 2014. Pentex's September sales were twice that of Marbro's. If Pentex's gross margin as a percentage of sales for September was 10%, Marbro's gross margin as a percentage of sales for the same period was: 10% 5% 20% Cannot be calculated