第1个回答 2016-11-14
31*99=31*(100-1)=31*100-31=3100-31=3069
第2个回答 2016-11-14
31x99
=31x(100-1)
=31x100-1x31
=3100-31
=3069本回答被提问者采纳
第3个回答 2016-11-14
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/3bf33a87e950352a7fa98d3e5a43fbf2b2118b38?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
看
追答谢谢
第4个回答 2016-11-14
31×99
=31×(100-1)
=3100-31
=3069
第5个回答 2016-11-14
=31*(100-1)
=31*100-31
=3100-31
=3069