How many pairs of whole numbers have a sum of 40

How many pairs of whole numbers equal the sum of 40?

Answer:

20

Step-by-step explanation:

1. 20+20
2. 21+19
3. 22+18
4. 23+17
5. 24+16
6. 25+15
7. 26+14
8. 27+13
9. 28+12
10. 29+11
11. 30+10
12. 31+9
13. 32+8
14. 33+7
15. 34+6
16. 35+5
17. 36+4
18. 37+3
19. 38+2
20. 39+1