估算:603×12≈ 398×57≈ 1000÷24≈ 89×79≈
口算。1+2= 0+6= 4+2= 2+3=2+4= 4+3= 1+6= 3+3=6+0= 2+4= 1+5=1+6= 5+1= 3+2=2+5= 3+2= 3+4=( )+6=7 4+( )=7 ( )+1=6 ( )+2=54+( )=6 ( )+5=7 ( )+3=7 5+( )=7
口算。( )+5=6 ( )+4=7 3+( )=7 ( )+2=54+( )=6 ( )+7=7 ( )+6=7 1+( )=66+( )=6 ( )+2=7 ( )-3=4 3+( )=72+5= 3+2= 3+4= 3+4=3+2= 5+1= 0+6= 3+1=5+1= 5+2= 5+1= 6+1= 4+3=
计算。5-4= 3-3= 4-2= 5-5= 4-1=5-0= 5-0= 1-0= 5-4= 5-2=5-3= 3-3= 5-5= 0-0= 5-2=3-2= 2-0= 4-3= 3-1= 4-1=
计算。5-3= 4-2= 3-2= 2-0= 3-2=3-2= 5-3= 2-2= 1-0= 4-1=5-3= 3-2= 4-1= 1-0= 3-2=0-0= 4-2= 5-1= 3-2= 5-5=
计算。1-0= 3-0= 4-2= 3-0= 2-0=3-1= 3-0= 5-3= 5-2= 4-1=4-2= 5-3= 5-4= 3-2= 5-4=5-2= 4-3= 1-0= 3-3= 3-1=