Who can do it in a simple way?

Who can do it in a simple way?

The original formula = 1 - (1-1 / 2) + 1-1 / 3 - (1-1 / 4) + 1-1 / 5 - (1-1 / 6) + 1-1 / 7 = 1 / 2-1 / 3 + 1 / 4-1 / 5 + 1 / 6-1 / 7 = 1 / 6 + 1 / 20 + 1 / 42 = 101 / 420

What is the simple method of 1 + 2-3-4 + 5 + 6-7-8 + 9 + 10 -... + 1990?

1+2-3-4+5+6-7-8+9+10-.+1990
=(1+2-3-4)+(5+6-7-8)+...+(1985+1986-1987-1988)+1989+1990
=-4*497+1989+1990
=-1988+1989+1990
=1991

16 / 3 by 9 by 27 / 8 = 11 / 4 by 14 / 13 by 26 / 7 = 5 / 2 by 25 / 2 by 2 / 5 = 5 / 4 by 8 / 3 by 9 / 5=
14 / 11 by 56 by 8 / 3 = 4 / 15 by 3 / 8 by 25 / 9 = I have counted the answers. Thank you for checking

16 / 3 times 9 times 27 / 8 = 162;
11 / 4 times 14 / 13 times 26 / 7 = 11;
5 / 2 times 25 / 2 times 2 / 5 = 25 / 2;
5 / 4 times 8 / 3 times 9 / 5 = 6;
14 / 11 times 56 times 8 / 3 = 11 / 6;
4 / 15 times 3 / 8 times 25 / 9 = 5 / 18;
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5 out of 7 x (7 out of 5 x 14)

Distribution law by multiplication