Sum of 1 to 100 Worksheet

Maths tricks trick 8: Add 1 to 100 in seconds · Set 251 · 40 questions

The trick (Pairs): Pair the first and last numbers: each pair adds to n + 1. Count the pairs — or multiply n × (n + 1) and halve it. Odd numbers 1 + 3 + 5 + …: count them and multiply that count by itself.

1. 1.1 + 2 + 3 + … + 39 =
2. 2.1 + 3 + 5 + … + 37 =
3. 3.1 + 3 + 5 + … + 23 =
4. 4.1 + 3 + 5 + … + 19 =
5. 5.1 + 2 + 3 + … + 29 =
6. 6.1 + 3 + 5 + … + 17 =
7. 7.1 + 2 + 3 + … + 7 =
8. 8.1 + 3 + 5 + … + 35 =
9. 9.1 + 2 + 3 + … + 19 =
10. 10.1 + 3 + 5 + … + 15 =
11. 11.1 + 3 + 5 + … + 39 =
12. 12.1 + 3 + 5 + … + 41 =
13. 13.1 + 2 + 3 + … + 20 =
14. 14.1 + 2 + 3 + … + 9 =
15. 15.1 + 2 + 3 + … + 65 =
16. 16.1 + 3 + 5 + … + 9 =
17. 17.1 + 2 + 3 + … + 25 =
18. 18.1 + 2 + 3 + … + 77 =
19. 19.1 + 2 + 3 + … + 86 =
20. 20.1 + 3 + 5 + … + 33 =
21. 21.1 + 2 + 3 + … + 89 =
22. 22.1 + 3 + 5 + … + 25 =
23. 23.1 + 2 + 3 + … + 59 =
24. 24.1 + 2 + 3 + … + 17 =
25. 25.1 + 2 + 3 + … + 27 =
26. 26.1 + 2 + 3 + … + 44 =
27. 27.1 + 2 + 3 + … + 26 =
28. 28.1 + 2 + 3 + … + 50 =
29. 29.1 + 3 + 5 + … + 31 =
30. 30.1 + 2 + 3 + … + 92 =
31. 31.1 + 2 + 3 + … + 53 =
32. 32.1 + 2 + 3 + … + 93 =
33. 33.1 + 2 + 3 + … + 73 =
34. 34.1 + 2 + 3 + … + 58 =
35. 35.1 + 2 + 3 + … + 45 =
36. 36.1 + 2 + 3 + … + 11 =
37. 37.1 + 2 + 3 + … + 33 =
38. 38.1 + 2 + 3 + … + 79 =
39. 39.1 + 3 + 5 + … + 45 =
40. 40.1 + 2 + 3 + … + 31 =

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