六年级简便计算题，在线等！！！

①99又34分之33除以17分之1
=(99X34+33)/34X17
=[(100-1)X34+33]/2
=(34X100-34+33)/2
=3399/2
=1699.5
②7/6+13/12+21/20+31/30+...+421/420
=1+1/6+1+1/12+...+1+1/420
=1+1/(2X3)+1+1/(3X4)+...+1+1/(20X21)
=1X19+1/2-1/3+1/3-1/4+...+1/20-1/21
=19+1/2-1/21
=19又42分之19

(1)原式=（100-1/34）×17
=1700-0.5
=1699.5

1. =100*1/17-1/13
=1699又12/13