To find the ratio of at-bats to hits, you can set it up as follows:
- Juan had 30 at-bats and 10 hits.
The ratio of at-bats to hits is calculated as:
\[ \text{Ratio of at-bats to hits} = \frac{\text{Number of at-bats}}{\text{Number of hits}} = \frac{30}{10} = 3:1. \]
So, the correct answer is:
D. 3:1