二、常见数学疑难几经解答思路
1.从2 3 4 5 6 7 8 9中取数字组成三位数号码,assign to 330 employee, 数字不重复, 问多少号码unassigned?
解:P==336
336-330=6
2.一个工作W,X做要比Y做少两天,X,Y一起做4/3W要3天,求X单独做2W要几天?
解:令W/X=x,W/Y=y,则x+2=y
/=3
两式连立化去y,即可解得x
3.=2^x3^y5^z 代表的是n的函数,x,y,z,都是positive integer, and x,y,z,分别代表n的百位,十位和个位,问如果f=9f,m-v=?
解:因为f=9f,所以两数百位个位都相同,令a为m的十位,b为n的十位则可知,/=9
解得a-b=2
所以m-v=210=20
4.10的n次方减38所得数的digit sum 为350. n=?
解:9+=350
5.1到n是连续整数, 1到n 数的乘积能被990 整除, 问n 最少是?
解:990=11109,所以n不能小于11
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