课件9张PPT。乘 车车上有2人2+3+2=57车上有7人7-3+2=46再见试一试5 + 2 - 3 7 - 2 - 3 4 + 1 + 5 8 - 3 + 4 ====745251059练一练1.说一说,算一算.=练一练2.7 + 2 - 8 =8 - 8 + 4 =10 - 4 + 2 =10 - 8 + 5 =10 - 7 - 3 =3 + 5 + 1 =2 + 7 + 1 =6 - 3 + 7 =3 + 5 - 6 =练一练4.2 + 2 + 2 + 2 + 2 =练一练4.9 - 2 - 2 - 2 - 2 =