请教各位几道数学~~谢谢

顿顿的微笑

If n is a positive integer and n² is divisible by 72, then the largest positive integer that must divide n is ()

答案是12

请问红色部分是什么意思？

A square countertop has a square tile inlay in the center, leaving an untiled strip of uniform width around the tile.  If the ratio of the tiled area to the untiled area is 25 to 39,which of the following could be the width, in inches, of the strip?

答案是1、3、4

这道题目我真的是没看懂，麻烦请人帮我解释一下~~~万分感谢

Jerome wrote each of the integers 1 throuth 20, inclusive, on a separate index card. He placed the cards in a box, then drew cards one at a time randomly from the box, without returning the cards he had already drawn to the box. In order th ensure that the sum of all the cards he drew was even, how many cards did Jderome have to draw?

答案是12

这道题目如果抽出来时5个奇数，7个偶数呢?和不是就不是偶数了？想不明白俄

以上几题是出自陈向东的数学~~真心求教各位，盼望有人可以帮助我~~~不甚感激

顿顿的微笑

拜托有人可以帮忙解答一下吗？

谢谢啦