口算。6-5= 5-1= 7-1=7-4= 3-3= 7-5=4-1= 6-3= 6-4=7-7= 7-2= 7-6=7-3= 6-3= 5-4=6-2= 7-2= 7-3=7-4= ( )-4=2 6-( )=2( )-3=4 6-( )=3 7-( )=3
7.9×11-7.9 0.99×9+0.99
199.8×19.99-199.9×19.97 (10-100÷10)×11=
4.83×0.59+0.41×1.59-0.324×5.9 (346-10)÷16-12
49×50≈ 89×41≈ 10×42≈ 20×32≈ 10×21≈ 30×32≈
估算:23×10≈ 49×10≈ 28×30≈ 38×10≈ 41×10≈ 42×10≈