7/12÷括号1/2+2/3括号乘2/5用递等式计算，能简算的要简算

7/12÷括号1/2+2/3括号乘2/5 =7/12÷（3/6+4/6）x2/5 =7/12÷7/6x2/5 =7/12x6/7x2/5 =1/2x2/5 =1/5