Final answer:
The common denominator for the mixed numbers 3 3/10 and 5 3/8 is 40, which is the least common multiple of their denominators, 10 and 8.
Step-by-step explanation:
The common denominator for the mixed numbers 3 3/10 and 5 3/8 is the least common multiple (LCM) of their denominators. The denominators here are 10 and 8. To find the LCM of 10 and 8, we list the multiples of each number until we find a common multiple. The multiples of 10 are 10, 20, 30, 40, and so on. The multiples of 8 are 8, 16, 24, 32, 40, and so on. We can see that the first common multiple is 40, which means the common denominator is 40.