在三位正整数的集合中有多少个数是7的倍数?答:7的倍数有 7,14,21,35,42,49,56,63,70,77,84,91,98,105,112,119,126,133,140,147,154,161,168,175,182,189,196,203,210,217,224,231,238,245,252,259,266,273,280,287,294,301,308,315,322,329,336,343,350 357,364,371,378,385,392,399,406,413,420……1、一个整数能够...