Here's the case: 10 is evenly divisible only by 2 and 5 (and, trivially, 1 and itself). 12 is divisible by 2, 3, 4, and 6, making it more often convenient to divide. This is why we still have 24 hours per day (often counted 1–12 twice), each divided into 60 (5*12) minutes, divided again into 60...