Plz help it's confusing me i will give brainliest

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

In the following situation, determine whether you are asked to determine the number of permutations or combinations. then do the calculation how many ways are there to pick a starting five from a basketball team of twelve members? a. permutation; ps - 2520 b. combination; 1c, - 792 c. combination: 2cs - 2520 d. permutation; ps - 95040

Anyone know? will mark brainliest if correct!