Question

简便计算20分之3+30分之3+42分之3+56分之3+72分之3

Answer 1

=3×(1/4×5+1/5×6+1/6×7+1/7×8+1/8×9)
=3×(1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9)
=3×(1/4-1/9)
=12分之5