Let's find the ages of the three brothers:
- Adeyemi is 15 years old.
- Ojo is 3 years younger than Adeyemi, so Ojo's age is: \[ 15 - 3 = 12 \text{ years old.} \]
- Olade is the eldest brother at 21 years old.
Now we have the ages:
- Adeyemi: 15 years
- Ojo: 12 years
- Olade: 21 years
To find the average age of the three brothers, we add their ages together and then divide by the number of brothers:
\[ \text{Total Age} = 15 + 12 + 21 = 48 \]
\[ \text{Average Age} = \frac{48}{3} = 16 \]
So, the average age of the three brothers is 16 years old.