①124+16×5
②540÷3×6
③500﹣906÷3
40×20=(4×10)×(2×10)=(4×2)×(10×10)=8×100=800
0.4×0.2=(4×0.1)×(2×0.1)=( × )×( × )= ×
=(4× )×(2× )=( × )×( × )= ×
(+)×9= 1.5×100= 99×0.8+0.8= 42=
+= 7﹣= ×= ÷=