巧算:
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmfenced%3E%3Cmrow%3E%3Cmn%3E1%3C%2Fmn%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmfrac%3E%3Cmrow%3E%3Cmn%3E1%3C%2Fmn%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmn%3E18%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmfrac%3E%3C%2Fmrow%3E%3C%2Fmfenced%3E%3Cmo%3E%C3%97%3C%2Fmo%3E%3Cmfenced%3E%3Cmrow%3E%3Cmn%3E1%3C%2Fmn%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmfrac%3E%3Cmrow%3E%3Cmn%3E1%3C%2Fmn%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmn%3E19%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmfrac%3E%3C%2Fmrow%3E%3C%2Fmfenced%3E%3Cmo%3E%C3%97%3C%2Fmo%3E%3Cmfenced%3E%3Cmrow%3E%3Cmn%3E1%3C%2Fmn%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmfrac%3E%3Cmrow%3E%3Cmn%3E1%3C%2Fmn%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmn%3E20%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmfrac%3E%3C%2Fmrow%3E%3C%2Fmfenced%3E%3C%2Fmath%3E)
【我思考】每个括号里的数相加后,前一个括号里的({#blank#}1{#/blank#})刚好与后一个括号里的({#blank#}2{#/blank#} )相同。
【我验证】
({#blank#}3{#/blank#})×({#blank#}4{#/blank#})=({#blank#}5{#/blank#})
({#blank#}6{#/blank#} )×( {#blank#}7{#/blank#})=({#blank#}8{#/blank#} )。
【我发现】计算结果是第一个括号里的数相加后的({#blank#}9{#/blank#} ),后一个括号里的数相加后的({#blank#}10{#/blank#} ),作为最后积的({#blank#}11{#/blank#} )。