估算:81÷2≈ 82÷4≈83÷8≈ 84÷2≈
6-3= 5-3= 6-6= 8-1= 9-1= 10-4=
8-4= 9-5= 5-5= 3-3= 7-7= 8-7=
9-4= 8-2= 9-7=4-4= 10-5= 4-2=
8-5= 10-3= 9-3=10-7= 7-5= 6-4=
7-4= 6-0= 5-2=10-9= 10-8= 8-2=