问题
单项选择题
Coins are to be put into 7 pockets so that each pocket contains at least one coin. At most 3 of the pockets are to contain the same number of coins, and no two of the remaining pockets are tO contain an equal number of coins. What is the least possible number of coins needed for the pockets ？（）
A．7
B．13
C．17
D．22
E．28
答案
参考答案：C
解析：
要使放入口袋中的硬币数目最少，就要使只放一个硬币的口袋的数目尽可能的多。根据题意可知，这样的口袋最多只有三个，而其余的四个口袋，则取尽可能小的且互不相同的正整数，分别为2，3，4，5。因此这些口袋中所需的最少硬币个数为3×1+2+3+4+5=17。