( 5/7乘 4/7)乘 59= 20/49 乘59= 20/49 乘 (49+10)= 20/49 乘 49+ 20/49乘 10= 20 + 200/49= 20 + 4又4/49= 24又4/49
简便运算,(5/7乘 4/7)×49=20/49×49=20
