What formula can you use to find the nth triangular number

The dolphins at the webster are fed 1/2 of a bucket of fish each day the sea otters are fed 1/2 as much fish as the dolphins how many buckets of fish are the sea fed each day? simplify you answer and write it as a proper fraction or as a whole or mixed number

Kristen is wrapping presents for the holidays. she has a box that measures 4 ft. x 2 ft. x 2 ft. how many square feet of wrapping paper does she need to cover the box without overlapping?

John kept track of how many baskets were made in a basketball game. after 4 minutes, 5 baskets were made. how many baskets were made between 9 and 10 minutes? a. 0 b. 1 c. 2 d. 3