5.6÷4-1.68×0.45 用简便计算5.6÷4-1.68×0.45=1.4-0.84×（2×0.45）=1.4-0.84×0.9=1.4-0.756=0.644
5.6÷4-1.68×0.45=1.4-0.84x2x0.45=1.4-0.84x0.9=1.4-0.756=0.644
