解决下列英语问题.补全对话:1、A:Hello,li lei!Can you___out and...答:2.both,vegetable,how,long,get,And,drink 3.better,waiting,start,3,1. e/go afraid feel wrong Nothing little see so have better 2. both vegetables how long have Any drink 3. better waiting start,2,解决下列英语问题.补全对话:1、A:Hello,li lei!Can you___out and play football...
统计所有四位正整数中各个数位上数字之和是9的数的个数答:统计所有四位正整数中各个数位上数字之和是9的数的个数 解:因为是四位正整数 所以首位不能为0 当首位为1时:有1008,1017,1026,1035,1044,...,1800 共有9+8+7+...+1=C(10,2)=45个 当首位为2时:有2007,2016,2025,2034,2043,...,2700 共有8+7+6+...+1=C(9,2)=36个 .....