0.325*0.8+0.55/5/4-3/5/8/7
=0.325*0.8+0.55*0.8-3/5×7/8
=（0.325+0.55）×0.8-3/5×7/8
=7/8×0.8-0.6×7/8
=7/8×（0.8-0.6）
=7/8×1/5
=7/40