[計量] problem solving

[bvejlg372661 (飛天摩人)]

If x and y are integers and xyy is a positive odd integer,
which of the following must be true?
Ⅰ. xy is positive.
Ⅱ. xy is odd.
Ⅲ. x + y is even.
(A) Ⅰ only
(B) Ⅱ only
(C) Ⅲ only
(D) Ⅰ and Ⅱ
(E) Ⅱ and Ⅲ

Ans:E

我有疑問的是Ⅲ

若x,y其中一奇數一偶數不是就不符合,怎還會成立?

感謝解答~m(_ _)m

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推 growthme:題目說:xyy is a positive odd integer，表XY 皆為奇數
→ growthme:因為 只要有一個偶數，他的乘積，就會變成偶數。
推 alberta:x和y鐵定都是奇數否則xyy不會是奇數的
→ bvejlg372661:感謝解答^^終於懂了~