2又7分之【4】除以28分之15乘以21分之5
= [18]/7 x28/15x5/21
= [18]/7x28/3x1/21
= [18]/7x4/9
=8/7
=1又1/7我是说2又7分之1除以28分之15乘以21分之52又7分之【1】除以28分之15乘以21分之5= 15/7 x28/15x5/21= 4x5/21= 20/21