51又3分之2÷3分之5+71又4分之3÷4分之7+91又5分之4÷5分之9=(51+2/3)÷(5/3)+(71+3/4)÷(7/4)+(91+4/5)÷(9/5)=(155/3)÷(5/3)+(287/4)÷(7/4)+(459)/5÷(9/5)=(155/3)×3/5+(287/4)×4/7+(459)/5×5/9=31+41+51=41...