Question

30+31+32+...+40

Answer 1

30 + 31 + 32 + ... + 40 = 355

Answer 2

Ta có:

1+2+3+...+29 = 29 .30 : 2 = 435

1+2+3+...40 = 40.41 : 2 = 820

=> [1+2+3+...+40] - [1+2+3+...+29] = 820-435

=> 30+31+32+...+40 = 385

Answer 3

30+31+32+...+40=(40+30).11:2=385