Tính nhanh
A= 1/1x2 + 1/2x3 + 1/3x4 +...+1/99x100
B= 3/1x4 + 3/4x7 + 3/7x10 +....+ 3/97x100
C= 3/1x3 + 3/3x5 + 3/5x7 +...+ 3/99x101
D= 1/4 + 1/28 + 1/70 +....+ 1/10300
E= 1/1x4 + 1/4x7 + 1/7x10 +...+ 1/52x55
F= 10 x (1/2 + 5/6 + 11/12 + 19/20 +...+ 89/90)
