Final answer:
The difference in ages between Derek and his youngest brother is 9.025 years.
Step-by-step explanation:
The difference in ages between Derek and his youngest brother can be found by subtracting their ages. Derek is 12.4 years old and his youngest brother is 2.375 years old. To find the difference, subtract 2.375 from 12.4:
12.4 - 2.375 = 9.025
So, the difference in their ages is
9.025
years.