(1)1/8+5/7+6.875+2/7=(1/8+6.875)+(5/7+2/7)=(0.125+6.875)+1=7+1=8 (2)=（1/3·3/2-1/3·2/5）·3/5 =1/2·3/5-1/3·2/5·3/5 =3/10-1/2 =-1/5
1/8+6.875=7然后在加上 （5/7+2/7=1)最后得8
6.875=6又7/8；第二题分母通分
