(12又4/9 +7又5/13 )÷(24又8/9 +14 又10/13)
=(12+4/9 +7+5/13 )÷(24+8/9 +14 +10/13)
发现前一括号内的所有项一一对应后括号内的所有项.都是差两倍
所以=2(12+4/9 +7+5/13 )÷(24+8/9 +14 +10/13)÷2
= (24+8/9 +14 +10/13)÷(24+8/9 +14 +10/13)÷2
=1/2)