199.7×19.98－199.8×19.96=199.7×19.98－19.98×199.6=19.98×(199.7-199.6)=19.98×0.1=1.998
199.7×19.98−199.8×199.6=199.7×19.98−19.98×199.6=19.98×(199.7−199.6)=19.98×0.1=1.998
