小数运算的速算和简算,1.2121212÷3.303033.3+3.33+3.333+3.3333+3.333331990×198.9-1989×198.860.7×0.60.45×172-0.9×71×0.5-0.45简算不是直接计算，这样我老早就直接用计算机算了

Question

小数运算的速算和简算,
1.2121212÷3.30303
3.3+3.33+3.333+3.3333+3.33333
1990×198.9-1989×198.8
60.7×0.6
0.45×172-0.9×71×0.5-0.45
简算不是直接计算，这样我老早就直接用计算机算了

Answer 1

1.2121212÷3.030303(怀疑此题抄丢一个零,故加上一个零)
=1.2*1.010101/3*1.010101
=0.4
3.3+3.33+3.333+3.3333+3.33333
=3*1.1+3*1.11+3*1.111+3*1.1111+3*1.11111
=3*(1.1+1.11+1.111+1.1111+1.11111)
=3*5.5432
1990×198.9-1989×198.8
=1990×198.9-(1990×198.8-198.8)
=1990×198.9-1990×198.8+198.8
=1990×(198.9-198.8)+198.8
=1990*0.1+198.8
=199+198.8
60.7×0.6
=(60+0.7)*0.6
=36+0.42
=36.42
0.45×172-0.9×71×0.5-0.45
=0.45×172-0.45×71-0.45
=0.45*(172-71-1)
=0.45*100
=45
用键盘写算式太费劲.有的题没计算到最后,计算到最后的答案也未必对.只是方法和思路应该是正确的.时间匆匆,有不准确的地方,见谅!