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1.25×0.25×8×40用简便方法计算 5.7×9.9 0.34×10.1

(10-0.1)*(10+0.1)

春怨(刘方平)乌衣巷(刘禹锡)

1.9×25+10.5×5 =1.9x5x5+10.5x5 =5x(1.9x5+10.5) =5x(9.5+10.5) =5x20 =100

10.1x8.9 =(10+0.1)x8.9 =10x8.9+0.1x8.9 =89+0.89 =89.89

解:因为 k(k+1)=k²+k 所以 1*2+2*3+3*4+4*5+5*6+6*7+7*8+8*9+9*10+10*11 ```` =1²+1+2²+2+3²+3+4²+4+5²+5+6²+6+7²+7+8²+8+9²+9+10²+10 ``` =1²+2²+3²+4²+5²+...

1.25X0.4X80X2.5 =(1.25×8×10)×(0.4×2.5) =10×10×1 =100 3.3X(1.7一5.9)直接算 0.8X(12.5一1.25) =0.8×12.5-0.8×1.25 =10-1 =9

1+2+3+4+5+6+7+8+9+10+…+100=100×(100+1)2=50×101=5050.

①12.8+ 7 20 +7.2+ 1 10 =(12.8+7.2)+( 7 20 + 1 10 ),=20+ 9 20 ,= 20 9 20 ;②9.9×35=(10-0.1)×35,=10×35-0.1×35,=350-3.5,=346.5;③10- 5 8 - 11 8 =10-( 5 8 + 11 8 ),=10-2,=8;④12.5×5×16=(12.5×8)×(5×2),=100×10,=...

计算下面各题,注意使用简便方法。 9/10×5/12+4/7+3/7 =3/8+(4/7+3/7) =3/8+1 =1又3/8 5/8×5/9+3/8×5/9 =(5/8+3/8)×5/9 =1×5/9 =5/9 13/10÷7+13/10×6/7 =13/10×1/7+13/10×6/7 =13/10×(1/7+6/7) =13/10×1 =13/10 24×(5/6-3/8) =24×5/6-24...

0.72x10.1 =0.72×(10+0.1) =0.72×10+0.72×0.1 =7.2+0.072 =7.272 9.98x9.9 =9.98×(10-0.1) =9.98×10-9.98×0.1 =99.8-0.998 =98.802 6.4x0.25x12.5 =(8×0.25)×(0.8×12.5) =2×10 =20 43x11.8十5.7x118 =43x11.8十57x11.8 =(43+57)x11.8 ...

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