看图
4/5-3/4+1/3+1/5-1/4=(4/5+1/5)-(3/4+1/4)+1/3=1-1+1/3=1/3。4/5-(7/8-1/5)=4/5-7/8+1/5=(4/5+1/5)-7/8=1-7/8=1/8。
