Question

简便计算，写出过程

30分之1+42分之1+56分之1+72分之1

Answer 1

原式=1/5*6+1/6*7+1/7*8+1/8*9
=(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)
=1/5-1/9
=4/45

Answer 2

1/30 + 1/42 + 1/56 + 1/72
=（1/5-1/6）+（1/6-1/7）+（1/7-1/8）+（1/8-1/9）
=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1/5-1/9
=4/45