2/3除5/8+1/3除5/8
=2/3乘8/5+1/3乘8/5
=(2/3+1/3)乘8/5
=1乘8/5
=8/5
7/12乘1/3+5/12除3
= 7/12乘1/3+5/12乘1/3
=(7/12+5/12)乘1/3
=1乘1/3
=1/3