小学数学很难吗？为什么很多孩子学不好数学？
巧妙地记住一些常用的数值，数学就会变得简单而有趣，做题的时候不用计算就能直接写出答案，能节省不少时间。这些数值背下来，以后到了中学，你会发现用处更大了呢~
一、常用分数、小数的互化
1/2 =0.5=50%
1/3 ≈0.333 =33.3%
2/3 ≈0.667=66.7%
1/4 =0.25=25%
3/4 =0.75=75%
1/5 =0.2=20%
2/5 =0.4=40%
3/5 =0.6=60%
4/5 =0.8=80%
1/6 ≈0.167=16.7%
5/6 ≈ 0.833=83.3%
1/8 =0.125=12.5%
3/8 =0.375=37.5%
5/8 =0.625=62.5%
7/8 =0.875=87.5%
1/9 ≈ 0.111=11.1%
1/10 =0.1=10%
1/20=0.05=5%
3/20=0.15=15%
7/20=0.35=35%
9/20=0.45=45%
11/20=0.55=55%
13/20=0.65 =65%
17/20=0.85=85%
19/20=0.95=95%
1/16 =0.0625=6.25%
1/32 =0.03125=3.125%
1/64 =0.015625=1.5625%
1/7 =0.142857142857…≈0.143 =14.3%
2/7 =0.285714285714…≈0.286=28.6%
3/7 =0.428571428571…≈0.429=42.9%
4/7 =0.57142857142…≈0.571=57.1%
5/7 =0.714285714285…≈0.714=71.4%
6/7 =0.857142857142…≈0.857=85.7%
熟记：142857
二、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
3.14×10=31.40
3.14×11=34.54
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
