9+10= 10+8= 2+10=10+0= 10+6= 10+4=
估算:865500-578900≈803433-205000≈455464-205000≈866546-578900≈70123-105000≈553543-305540≈
口算:831500-554900=25650+21560=95410+21260=1249000-249000=2580010-2580000=246000+154000=
口算:865500-578900=95400+21560=258000-158000=125000+125000=3571000-2571000=2514980-2414980=
估算:205833-125000≈305533-125000≈3035433-205000≈862500-578900≈95453+21554≈3033533-204580≈
口算:369500-256900=652000-325600=869500-556900=854000-625600=4512000-4500000=1526000+1574000=