Let's define set S by 3(屬於)S ; a+b(屬於)S if a(屬於)S and b(屬於)S
Which of the following statements is true?
(a) S is a empty set
(b) S is the set of integers that are not divisible by 3
(c) S is the set of positive integers divisible by 3
(d) S is the set of all positive integers
(e) None of the above
我看解答給的答案是C，想說只有那三個條件怎麼能確定都是3的倍數呢
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One hundred students enter a locker room that contains 100 lockers.
The first student open all the lockers.The second student changes the
status(from open to closed, and vice versa) of every other locker,
starting with the second locker.The third student then changes the
status of every third locker,starting with the third locker.In general,
for 1<=K<=100,the kth student changes the status of every kth locker,
starting with the kth locker.After the 100th student has gone through
the lockers,which lockers are left open?
想問一下這題大家會怎麼解?
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