To find the total distance from Duncan's starting point on the diving board to his lowest point beneath the surface of the pool, we can break down the calculation as follows:
- Starting point on the diving board: Duncan is 5 feet above the surface of the pool.
- Lowest point beneath the surface: Duncan is 7 feet below the surface of the pool.
First, we need to find the distance from the diving board to the surface of the pool. This is simply the height of the diving board above the pool, which is 5 feet.
Next, we need to find the distance from the surface of the pool to the lowest point Duncan reaches below the surface. Since he goes down 7 feet below the surface, this distance is 7 feet.
Now, we add these two distances together to find the total distance he travels:
\[ \text{Total Distance} = \text{Distance from board to surface} + \text{Distance from surface to lowest point} \] \[ \text{Total Distance} = 5 \text{ feet} + 7 \text{ feet} = 12 \text{ feet} \]
Thus, the total distance from Duncan's start on the diving board to his lowest point beneath the surface of the pool is \( \boxed{12} \) feet.