人教版三年级数学下册笔算乘法(不进位).ppt

观察(guānchá)比较 用第二个乘数每一位上的数分别 去乘第一个乘数每一位上的数。乘得的积要分别和乘数的个位和十位对齐。再把两次乘积相加。 8 1 6 8 × 1 2 1 4 4 2 1 2 × 1 4 8 2 今天(jīntiān)学习的 以前(yǐqián)学习的 第十页，共14页。 笔算乘法(chéngfǎ)（不进位） 两位数乘两位数 第一页，共14页。 竖式计算(jì suàn) 1 4 2 8 2 2 3 1 3 3 9 6 多位数乘一位数，要用一位数分别去乘多位数每一位上的数。 × × 第二页，共14页。 口算 20×20= 24×10= 40×50= 12×30= 400 360 2000 240 第三页，共14页。 每套书有14本，王老师买了12套。一共(yīgòng)买了多少本？ 第四页，共14页。 ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· 点子(diǎn zi)图方案 6套 6套 先算出6套书的数量(shùliàng) 再算出2个6套书的数量(shùliàng) 14×6=84（本） 84×2=168（本） 第五页，共14页。 点子(diǎn zi)图方案 4套 先算出4套书的数量(shùliàng) 再算出3个4套书的数量(shùliàng) ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· 4套 4套 14×4=56（本） 56×3=168（本） 第六页，共14页。 点子(diǎn zi)图方案 10套 先算出10套书的数量(shùliàng) 再算出2套书的数量(shùliàng) ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· 2套 140+28=168（本） 14×10=140（本） 14×2=28（本） 第七页，共14页。 ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· ·············· 点子(diǎn zi)图方案比较 ① ② ③ 14×6=84（本） 84×2=168（本） 14×4=56（本） 56×3=168（本） 14×10=140（本） 14×2=28（本） 140+28=168（本） 第八页，共14页。 探究(tànjiū)竖式写法 14×12＝ 1 6 8 × 1 2 1 4 8