五奥第十三讲小数的速算与巧算(1) (付倩)

5×4.73×0.125×320 (6)99.6+99.8+99.9+100+100.1 Р=0.25×40×0.125×8×4.73 =100-0.4+100-0.2+100-0.1+100+100+0.1Р=47.3 =499.4Р(7)100×7.9+184×2.1+84×2.9 Р =100×7.9+100×2.1+84×2.1+84×2.9Р=100×10+84×5Р=1420РB组训练题Р(1)4.7×2.8+3.6×9.4 (2)6.3×27+1.9×21Р=4.7×2.8+7.2×4.7 =21×8.1+21×1.9Р=47 =210Р(3)3.75×4.8+62.5×0.48 (4)1250×0.037+0.125×160+12.5×2.7Р=4.8×10 =12.5×3.7+12.5×1.6+12.5×2.7Р=48 =12.5×8=100Р(5)3.6×232-36×13.2-360 (6)3.42×76.3+7.63×57.6+9.18×23.7Р =3.6×(232-132-100) =76.3×(3.42+5.76)+9.18×23.7Р =0 =(76.3+23.7)×9.18=918РC组训练题Р(1)1.23×2.45-1.22×2.46Р=1.22×2.45+0.01×2.45-1.22×2.46Р=0.0245-0.0122Р=0.0123Р(2)(0.1+0.12+0.123+0.1234)×(0.12+0.123+0.1234+0.12345)-(0.1+0.12+0.123+0.1234 +0.12345)×(0.12+0.123+0.1234)Р 设 0.12+0.123+0.1234 = aР 原式=(0.1+a)×(0.1+0.12345)-(0.1+a+0.12345)×aР =0.1×0.12345Р =0.012345