请教两道DS PREP题~~~

If w, x, y, and z are integers such that w/x and y/z are integers, is wx+yz odd?

(1) wx + yz is odd.

(2) wz + xy is odd.

Answer: B

我选D， PREP上关于（1）的解释是这样的：

(1) suppose wx is odd, either w or x or both could be odd. If w and x are both odd, ws is odd. If w is even and x is odd, wx is even.

可是要 wx 是奇数，不是得两个奇数相乘才能得到么？怎么能一奇一偶呢？

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2-216.

(1) suppose wx is odd, either w or x or both could be odd. If w and x are both odd, ws is odd. If w is even and x is odd, wx is even.

可是要 wx 是奇数，不是得两个奇数相乘才能得到么？怎么能一奇一偶呢？

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2-216.

(1)  The product of the digits in n is 30.

(2)  The sum of the digits in n is 10.
                

Answer: C

我选A，PREP解释：

（1）30=2x3x5或6x5 所以此種情況下n有可能等於235，253，325，352，523，532或650，560，在前面的情況，n<550但在第二種情況，n>550，所以不充分。

650，560明显不满足 product of the digits is 30 啊。

不知道是哪里出了问题呢，望NN指点！

哦~原来是这样，只分解了，忘了别的factor了。。。谢谢啦！

那第一题呢？