Question

求1到300之间(包含1和300之内)既不能被3和5,也不能被7整除的数有多少?

Answer 1

问：求1到300之间(包含1和300之内)既不能被3和5,也不能被7整除的数有多少?

答：亲亲，你好，首先求出能被3或5整除的数和能被7整除的数，然后将它们在1到300之间的倍数位置上标记出来，最后统计没有被标记的数字即可。

答：其中能被3或5整除的数为 3,5,6,9,10,12,15,18,20,21,24,25,27,30,33,35,36,39,40,42,45,48,50,51,54,55,57,60,63,65,66,69,70,72,75,78,80,81,84,85,87,90,93,95,96,99,100,102,105,108,110,111,114,115,117,120,123,125,126,129,130,132,135,138,140,141,144,145,147,150,153,155,156,159,160,162,165,168,170,171,174,175,177,180,183,185,186,189,190,192,195,198,200,201,204,205,207,210,213,215,216,219,220,222,225,228,230,231,234,235,237,240,243,245,246,249,250,252,255,258,260,261,264,265,267,270,273,275,276,279,280,282,285,288,290,291,294,295,297,300；

答：能被7整除的数为7,14,21,28,35,42,49,56,63,70,77,84,91,98,105,112,119,126,133,140,147,154,161,168,175,182,189,196,203,210,217,224,231,238,245,252,259,266,273,280,287,294。将它们在1到300之间的倍数位置上标记，1-300之间不能被3、5、7整除的数字为未被标记的数字，可以直接数出来，一共有 119 个。