1. 直接写出得数。
$7.2×3=$ $12.5×0=$ $0.5×0.75=$
$16.1×0.2=$ $0×6.5=$ $1.2×0.6=$
$0.5×0.04=$ $0.08×100=$ $7.9×100=$
$2.5×4=$ $2.4×5=$ $0.4+8.7=$
$9-7.7=$ $1-0.999=$ $0.68×100=$
$45÷1000=$ $0÷72=$ $1.68÷10×10=$

$7.2×3=21.6$
$12.5×0=0$
$0.5×0.75=0.375$
$16.1×0.2=3.22$
$0×6.5=0$
$1.2×0.6=0.72$
$0.5×0.04=0.02$
$0.08×100=8$
$7.9×100=790$
$2.5×4=10$
$2.4×5=12$
$0.4+8.7=9.1$
$9-7.7=1.3$
$1-0.999=0.001$
$0.68×100=68$
$45÷1000=0.045$
$0÷72=0$
$1.68÷10×10=1.68$

2. 判断，对的画“√”，错的画“×”，并改正。
(1)$7.5+2.5×1.2$ 改正：
$=10×1.2$
$=12$
()
(2)$8×(0.4+12.5)×5$ 改正：
$=8×12.5+0.4×5$
$=100+2$
$=102$
()

(1) ×
改正：
7.5+2.5×1.2
=7.5+3
=10.5
(2) ×
改正：
8×(0.4+12.5)×5
=(8×5)×(0.4+12.5)
=40×12.9
=516

3. 计算下列各题，能简算的要简算。
$0.25×9.87×4$ $5.81×5.6+2.19×5.6$
$12.56÷5÷0.4$ $32×12.5×2.5$
$15.5×16.3+3.7×15.5$ $32×0.4×0.25×1.25$

$0.25×9.87×4$
$=0.25×4×9.87$
$=1×9.87$
$=9.87$
$5.81×5.6+2.19×5.6$
$=(5.81+2.19)×5.6$
$=8×5.6$
$=44.8$
$12.56÷5÷0.4$
$=12.56÷(5×0.4)$
$=12.56÷2$
$=6.28$
$32×12.5×2.5$
$=(8×12.5)×(4×2.5)$
$=100×10$
$=1000$
$15.5×16.3+3.7×15.5$
$=15.5×(16.3+3.7)$
$=15.5×20$
$=310$
$32×0.4×0.25×1.25$
$=(8×1.25)×(4×0.25)×0.4$
$=10×1×0.4$
$=4$