Final answer:
The smallest secret number Diane could be thinking of that is divisible by both 12 and 8 is 24, which is their least common multiple (LCM).
Step-by-step explanation:
The student asked for the smallest number that is divisible by both 12 and 8. Since 12 and 8 have common factors, we will have to find their least common multiple (LCM). The prime factorization of 12 is 2³ × 3 and the prime factorization of 8 is 2³. The LCM is the highest power of the prime factors involved, which in this case is 2³ × 3 = 24. Hence, the smallest number that Diane could be thinking of is 24, as it is the smallest number divisible by both 12 and 8.