Question

巧算下题 2分之3减去6分之5加上12分之7减去20分之9加上30分之11减去42分之13

Answer 1

3/2-5/6+7/12-9/20+11/30-13/42
=(1+1/2)-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)
=1+1/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7
=1-1/7
=7分之6