3分之4-12分之7+20分之9-30分之11+42分之13-56分之15简便运算

答：
4/3-7/12+9/20-11/30+13/42-15/56
=4/3-7/(3*4)+9/(4*5)-11/(5*6)+13/(6*7)-15/(7*8)
=4/3-7/3+7/4+9/4-9/5-11/5+11/6+13/6-13/7-15/7+15/8
=-1+4-4+4-4+15/8
=7/8

4/3-7/12+9/20-11/30+13/42-15/56
=4/3-(1/3+1/4)+1/4+1/5-(1/5+1/6)+1/6+1/7-(1/7+1/8)
=1-1/8
=7/8