natural numbers-counting numbers: 1,2,3,4,5...
whole numbers- natural numbers and zero
integers- whole numbers and negative numbers
ratioal numbers, number that can be written in form a/b where b≠0
irrational numbers- rational numbers and numbers that can't be written in form a/b, example is pi
real numbers is all of the above
complex numbers is none of the above, like √-1
so
-20 is an integer, a ratioal number, a real number