常用分数、小数的互化12 =0.5=50 ℅14 =0.25=25 ℅34 =0.75=75 ℅15 =0.2=20 ℅25 =0.4=40 ℅35 =0.6=60 ℅45 =0.8=80 ℅18 =0.125=12.5℅38 =0.375=37.5 ℅58 =0.625=62.5 ℅78 =0.875=87.5 ℅120 =0.05 320 =0.15 720 =0.35 920 =0.45 1120 =0.55 1320 =0.65 1720 =0.85 1920 =0.95 116 =0.0625 132 =0.03125 164 =0.015625 1128 =0.0078125 1256 =0.00390625 1512 =0.001953125 11024 =0.0009765625 13 ≈0.333 23 ≈0.667 16 ≈0.167 56 ≈0.833 17 =0.142857142857142857 ⋯⋯ ≈0.143 27 =0.285714285714285714 ⋯⋯ ≈0.286 37 =0.428571428571428571 ⋯⋯ ≈0.429 47 =0.571428571428571428 ⋯⋯ ≈0.571 57 =0.714285714285714285 ⋯⋯ ≈0.714 67 =0.857142857142857142 ⋯⋯ ≈0.857熟记： 142857 常用圆周率的计算3.14 ×1=3.14 3.14×2=6.28 3.14 ×3=9.42 3.14×4=12.56 3.14 ×5=15.70 3.14×6=18.84 3.14 ×7=21.98 3.14×8=25.12 3.14 ×9=28.26 3.14×12=37.68 3.14 ×16=50.24 3.14×18=56.52 3.14 ×20=62.80 3.14×25=78.50 3.14 ×32=100.48 3.14×36=113.04 3.14 ×49=153.86 3.14×64=200.96 3.14 ×81=254.34 3.14×121=379.94 常用的平方数12=1 22=4 32=9 42=16 52=25 62=36 72=49 82=64 92=81 102=100 112=121 122=144 132=169 142=196 152=225 162=256 172=289 182=324 192=361 202=400 常用的立方数13=1 23=8 33=27 43=64 53=125 63=216 73=343 83=512 93=729 103=1000 113=1331 123=1728 133=2197 143=2744 153=3375 163=4096 173=4913 183=5832 193=6859 203=8000约分时常用的乘法算式11×2=22 12×2=24 12×3=36 12×4=48 12×5=60 12×6=72 12×7=84 12×8=96 13×2=26 13×3=39 13×4=52 13×5=65 13×6=78 13×7=91 14×2=28 14×3=42 14×4=56 14×5=70 14×6=84 14×7=98 15×2=30 15×3=45 15×4=60 15×5=75 15×6=90 16×2=32 16×3=48 16×4=64 16×5=80 16×6=96 17×2=34 17×3=51 17×4=68 17×5=85 18×2=36 18×3=54 18×4=72 18×5=90 19×2=38 19×3=57 19×4=76 19×5=95 21×2=42 21×3=63 21×4=84 21×5=105 21×6=126 21×7=147 22×2=44 22×3=66 22×4=88 22×5=110 23...
