20
the numbers that make 18 mulitplyed together are 1,2,3,6,9 ect
37
1 and 18 2 and 9 3 and 6
1, 2 and 18 (when multiplied together) 1, 2 and 33 (when added together) In each case, there are infinitely more alternatives.
20
the numbers that make 18 mulitplyed together are 1,2,3,6,9 ect
-19 + 1 = -18
-1 and 18
18
2, 3 and 13
-3 and 6
21
Assuming you mean consecutive numbers, the answer is 5, 6 and 7.
That's obviously impossible. There is no answer. :P
56
37