what is 13 decreased by 3 time a number is 16

Answer 1

The wording of the question is a bit misleading ... usually "decreased by" means to make a quantity less, but in this problem, the solution is n = -1, so -3*n is -3 * (-1) which is positive 3, which usually means "increased by".

To avoid this confusion, I would prefer to see the question worded something like: "13 minus 3 times a number is 16".

Answer 2

In algebraic terms:

13 - 3n = 16