A conference planner has put together 280 binders for attendees and another 31 binders for presenters. How many total binders did the planner put together?

To find the total number of binders the conference planner put together, you need to add the number of binders for attendees to the number of binders for presenters. This means taking the 280 binders intended for attendees and adding the 31 binders designated for presenters.

The calculation is straightforward:

280 (binders for attendees) + 31 (binders for presenters) = 311 total binders.

This sum shows that the conference planner organized a cumulative total of 311 binders for both attendees and presenters. Thus, the answer is indeed 311, confirming that the choice selected is correct.