To determine how many boxes the volunteers packed per minute, you can divide the total number of boxes packed by the total time it took to pack them.
They packed 50 boxes in 20 minutes.
\[ \text{Boxes per minute} = \frac{\text{Total boxes}}{\text{Total time (in minutes)}} \]
\[ \text{Boxes per minute} = \frac{50 \text{ boxes}}{20 \text{ minutes}} = 2.5 \text{ boxes per minute} \]
So, the correct response is:
2.5 boxes/minute.