the number 12 is the smallest number that has four factors (2, 3, 4, 6). if one divide the numbers 10 and 12 with 3, the results will be 3.333... and 4, respectively. doing the same thing with 6, the results will be 1.666... and 2. doing the same thing with 5, the results will be 2 and 2.4. so, the duodecimal system can't control the fractions better than the decimal system.