30/1+42/1+50/1+72/1求简算有过程滴

...写反了吧,而且中间那个你确定是50不是56?
如果要有简算的题应该是这样吧
1/30+1/42+1/56+1/72
=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)
=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1/5-1/9
=4/45