数学不好，急切各位大侠指导2道数学题

yoo_hoo

这些题都是OG上的题，虽然有解释，可我还是搞不懂，望各位指教，谢谢！

    1. 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 ?
  I. 3/2    II. 3   III.  9/2

  A.I only   B. II only    C.I and II only   D. I and III only    E. I, II and III
我知道了这个面积比是5：8，那怎么能推出答案是 E 呢？

    2.If n is a positive integer and n平方 is divisible by 72, then the largest positive integer that must divide n is
    A.6     B.12    C.24     D.36     E.48
   这道题里的 is divisible by 72=is divided by？ 是N平方除以72呢还是72除以N平方啊？the largest positive integer that must divide n 怎么理解啊？
再次感谢相帮的网友

yoo_hoo

谢谢上面的指点，我是这样理解的，第一题给了你比率，所以任何的答案都是可能的，是吧；那第二题我当初做的也是E，可答案却是B，所以还是搞不懂该问题逗号后的意思是指什么，望大家能再给我指点一下，万分感谢！