二、奇數(shù)與偶數(shù)和的奇偶性

1、第二單元 因數(shù)與倍數(shù)奇數(shù)與偶數(shù)和的奇偶性奇數(shù)與偶數(shù)和的奇偶性把下面各數(shù)分別填在合適的圈內(nèi)。把下面各數(shù)分別填在合適的圈內(nèi)。27 48 53 207 420 801 8978奇數(shù)奇數(shù)偶數(shù)偶數(shù)5327207801484208978說說你是怎么判斷的？說說你是怎么判斷的？在整數(shù)中，是在整數(shù)中，是2的倍數(shù)的的倍數(shù)的數(shù)就是偶數(shù)，否則就是數(shù)就是偶數(shù)，否則就是奇數(shù)。奇數(shù)。個(gè)位上是個(gè)位上是0,2,4,6,8的數(shù)是的數(shù)是偶數(shù)；個(gè)位上是偶數(shù)；個(gè)位上是1,3,5,7,9的數(shù)是奇數(shù)。的數(shù)是奇數(shù)。 一、復(fù)習(xí)導(dǎo)入，揭示課題一、復(fù)習(xí)導(dǎo)入，揭示課題奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與

2、奇數(shù)的和是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？奇數(shù)奇數(shù)偶數(shù)偶數(shù)奇數(shù)奇數(shù)? ?偶數(shù)？偶數(shù)？奇數(shù)奇數(shù)奇數(shù)奇數(shù)奇數(shù)？奇數(shù)？偶數(shù)？偶數(shù)？偶數(shù)偶數(shù)偶數(shù)偶數(shù)奇數(shù)？奇數(shù)？偶數(shù)？偶數(shù)？從題目中你知道了什么？從題目中你知道了什么？題目讓我們對(duì)奇題目讓我們對(duì)奇數(shù)、偶數(shù)的和作數(shù)、偶數(shù)的和作一些探索。一些探索。我把問題表示我把問題表示成這樣成這樣 二、探究新知二、探究新知閱讀與理解閱讀與理解我隨便找?guī)讉€(gè)奇數(shù)、偶我隨便找?guī)讉€(gè)奇數(shù)、偶數(shù)，加起來看一看。數(shù)，加起來看一看。奇數(shù)：奇數(shù)：5， 7， 9， 11，偶數(shù)：偶數(shù)：8，12，20，24，581378155712791681220122436

3、奇數(shù)偶數(shù)奇數(shù)奇數(shù)偶數(shù)奇數(shù)奇數(shù)奇數(shù)偶數(shù)奇數(shù)奇數(shù)偶數(shù)偶數(shù)偶數(shù)偶數(shù)偶數(shù)偶數(shù)偶數(shù)奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？你怎么想？你怎么想？ 二、探究新知二、探究新知分析與解答分析與解答奇數(shù)除以奇數(shù)除以2余余1奇數(shù)：奇數(shù)：偶數(shù)：偶數(shù)：偶數(shù)除以偶數(shù)除以2沒有余數(shù)沒有余數(shù)奇數(shù)加偶數(shù)的和除以奇數(shù)加偶數(shù)的和除以2 2還余還余1 1，所以，奇數(shù)偶數(shù)奇數(shù)。，所以，奇數(shù)偶數(shù)奇數(shù)。奇數(shù)加奇數(shù)的和除以奇數(shù)加奇數(shù)的和除以2 2沒有余數(shù)，所以，奇數(shù)奇數(shù)偶數(shù)。沒有余數(shù)，所以，奇數(shù)奇數(shù)偶數(shù)。偶數(shù)加偶數(shù)的和除以偶數(shù)

4、加偶數(shù)的和除以2 2沒有余數(shù)，所以，偶數(shù)偶數(shù)偶數(shù)。沒有余數(shù)，所以，偶數(shù)偶數(shù)偶數(shù)。奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？你怎么想？你怎么想？ 二、探究新知二、探究新知分析與解答分析與解答奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？奇數(shù)偶數(shù)奇數(shù)偶數(shù)奇數(shù)奇數(shù)奇數(shù)奇數(shù)偶數(shù)偶數(shù)偶數(shù)偶數(shù)奇數(shù)奇數(shù)偶數(shù)偶數(shù)偶數(shù)偶數(shù)所以，同學(xué)們所以，同學(xué)們的結(jié)論是的結(jié)論是 二、探究新知二、探究新知奇數(shù)

5、與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和奇數(shù)與偶數(shù)的和是奇數(shù)還是偶數(shù)？奇數(shù)與奇數(shù)的和是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的和呢？534319853所以，奇數(shù)偶數(shù)奇數(shù)。所以，奇數(shù)偶數(shù)奇數(shù)。這個(gè)結(jié)論正確嗎？這個(gè)結(jié)論正確嗎？我可以再找一些我可以再找一些大數(shù)試一試。大數(shù)試一試。同學(xué)們還有其他方法嗎？同學(xué)們還有其他方法嗎？你覺得哪種方法好？你覺得哪種方法好？ 二、探究新知二、探究新知回顧與反思回顧與反思1.30名學(xué)生要分成甲、乙兩隊(duì)。如果甲隊(duì)人數(shù)為奇數(shù)，乙隊(duì)名學(xué)生要分成甲、乙兩隊(duì)。如果甲隊(duì)人數(shù)為奇數(shù)，乙隊(duì)人數(shù)為奇數(shù)還是偶數(shù)？如果甲隊(duì)人數(shù)為偶數(shù)呢？人數(shù)為奇數(shù)還是偶數(shù)？如果甲隊(duì)人數(shù)為偶數(shù)呢？30是偶數(shù)，甲隊(duì)人數(shù)為奇是偶數(shù)，甲隊(duì)人數(shù)為奇數(shù)，奇數(shù)奇數(shù)偶數(shù)，數(shù)，奇數(shù)奇數(shù)偶數(shù)，所以，乙隊(duì)人數(shù)為奇數(shù)。所以，乙隊(duì)人數(shù)為奇數(shù)。30是偶數(shù)，甲隊(duì)人數(shù)為偶是偶數(shù)，甲隊(duì)人數(shù)為偶數(shù)，偶數(shù)偶數(shù)偶數(shù)，數(shù)，偶數(shù)偶數(shù)偶數(shù)，所以，乙隊(duì)人數(shù)為偶數(shù)。所以，乙隊(duì)人數(shù)為偶數(shù)。 三、知識(shí)運(yùn)用三、知識(shí)運(yùn)用2. 奇數(shù)與奇數(shù)的積是奇數(shù)還是偶數(shù)？奇數(shù)與偶數(shù)的奇數(shù)與奇數(shù)的積是奇數(shù)還是偶數(shù)？奇數(shù)與偶數(shù)的 積是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的積呢？積是奇數(shù)還是偶數(shù)？偶數(shù)與偶數(shù)的積呢？5315774956307856886