31Ⅹ49+68Ⅹ49+49=49×(31+68+1)=49×100=4900
31×49+68×49+49=(31+68+1)×49=100×49=4900
31X49+68x49+49=(31+68+1)ⅹ49=100x494900
31X49+68X49+49=(31+68+1)X49=4900
=49×(31+68+1)=4900