Steve plants ten trees every three minutes. If he continues planting at the same rate, how long will it
take him to plant 2500 trees?

$\textbf{(A)}\ 1~1/4 \qquad \textbf{(B)}\ 3 \qquad \textbf{(C)}\ 5 \qquad \textbf{(D)}\ 10 \qquad \textbf{(E)}\ 12~1/2$
1. First, determine the rate at which Steve plants trees. He plants 10 trees every 3 minutes.
2. Calculate the number of trees Steve plants in one minute:
   \[
   \text{Trees per minute} = \frac{10 \text{ trees}}{3 \text{ minutes}} = \frac{10}{3} \text{ trees per minute}
   \]
3. Next, calculate the number of trees Steve plants in one hour (60 minutes):
   \[
   \text{Trees per hour} = \left(\frac{10}{3} \text{ trees per minute}\right) \times 60 \text{ minutes} = \frac{10 \times 60}{3} = 200 \text{ trees per hour}
   \]
4. Now, determine how many hours it will take Steve to plant 2500 trees:
   \[
   \text{Time in hours} = \frac{2500 \text{ trees}}{200 \text{ trees per hour}} = 12.5 \text{ hours}
   \]
5. Convert 12.5 hours to a mixed number:
   \[
   12.5 \text{ hours} = 12 \frac{1}{2} \text{ hours}
   \]

Thus, it will take Steve 12.5 hours to plant 2500 trees.

The final answer is $\boxed{12 \frac{1}{2}}$