1. 直接写出得数。
$400×50=$
$1 - 0.79=$
$8×8÷8×8=$
$0.21×0.3=$
$8.9×0.02=$
$2×0.32=$
$0.9×9.1=$
$0.32×100=$
$0.23×0.5=$
$3.6×1000=$
$50×6.5=$
$2.35×1=$
$120÷10=$
$5.2 - 5.2=$
$4.87 - 1.02=$
$2.2 - 1.5=$
$5 - 2.5=$
$0.24×4=$

$400×50=20000$
$1 - 0.79=0.21$
$8×8÷8×8=64$
$0.21×0.3=0.063$
$8.9×0.02=0.178$
$2×0.32=0.64$
$0.9×9.1=8.19$
$0.32×100=32$
$0.23×0.5=0.115$
$3.6×1000=3600$
$50×6.5=325$
$2.35×1=2.35$
$120÷10=12$
$5.2 - 5.2=0$
$4.87 - 1.02=3.85$
$2.2 - 1.5=0.7$
$5 - 2.5=2.5$
$0.24×4=0.96$

2. 计算下面各题，能简算的要简算。
$1.28×8.6 + 7.2×0.86$
$18×0.75 - 3.93$
$18.5 + 4.1×7.2 - 9.59 + 7.6$
$2.8×103 - 2.8×3$
$2.6×3.2 + 6.8×2.6$
$6.3 + (7.6 - 7.18)$
$1.25×0.25×32$
$10 - 0.64 - 0.36$
$7.9×5 - 2.9×5$
$37×99 + 37$

1.28×8.6 + 7.2×0.86
=1.28×8.6 + 0.72×8.6
=(1.28+0.72)×8.6
=2×8.6
=17.2
18×0.75 - 3.93
=13.5 - 3.93
=9.57
18.5 + 4.1×7.2 - 9.59 + 7.6
=18.5 + 29.52 - 9.59 + 7.6
=26.1 + 29.52 - 9.59
=55.62 - 9.59
=46.03
2.8×103 - 2.8×3
=2.8×(103-3)
=2.8×100
=280
2.6×3.2 + 6.8×2.6
=2.6×(3.2+6.8)
=2.6×10
=26
6.3 + (7.6 - 7.18)
=6.3 + 0.42
=6.72
1.25×0.25×32
=1.25×0.25×8×4
=(1.25×8)×(0.25×4)
=10×1
=10
10 - 0.64 - 0.36
=10-(0.64+0.36)
=10-1
=9
7.9×5 - 2.9×5
=(7.9-2.9)×5
=5×5
=25
37×99 + 37
=37×(99+1)
=37×100
=3700