乘除法的巧算
用简便方法计算下面各题
1、25×8×2
2、37×9×10
3、25×64×125×5
4、125×125×64
5、32×25×125
6、56×125
7、16×25×5
例3：计算：1200÷25÷4
用简便方法计算下面的题目
6000÷125÷85200÷4÷25 6300÷4÷75 4200÷8÷25
巧算：
333÷37÷31000000÷8÷125÷25÷8÷5例4：计算：12÷5+13÷532÷3－20÷3
用简便方法计算下面的题目
63÷8+9÷852÷5-7÷5
9÷13+6÷13+11÷1337÷9-11÷9-8÷91000000÷8÷125÷25÷8÷5
例5：计算：120×80÷60
技巧：四则元算中，若是同级运算，可以“带着符号搬家”（符号在前，数字在后）。

用简便方法计算下面的题目
28×25÷732×125÷4120×260÷120
45×37÷1563÷8×64÷7
9÷13+6÷13+11÷1337÷9-11÷9-8÷9
例6：计算：25÷10×4
技巧：四则运算中，若是同级运算，可以“带着符号搬家”（符号在前，数字在后）。

用简便方法计算下面的题目
6÷10×58÷20×1255÷6×6125÷4×8
9÷10×100÷945×25÷5÷945×37÷1563÷8×64÷7
特殊的两位的乘法
1、十几乘十几。

口诀：头乘头，尾加尾，尾乘尾。

注：个位相乘，不够两位数要用0占位。

例：12×14=？解: 1×1=1 2＋4＝6 2×4＝8 12×14=168
练习：15×13= 14×12= 12×15= 19×17= 16×14=
２、头同，尾合十。

口诀：一个头加１后头乘头，尾乘尾，个位相乘不够两位数用0占位。

例：23×27=？解：2＋1＝3 2×3＝6 3×7＝21 23×27=621
练习：34×36= 82×88= 51×59= 24×26= 74×76=
3、尾同，头合十。

口诀：十位相乘加个位放百位，个位相乘不够两位数用0占位。

例：34×74=？解： 3×7＋4=25 4×4=16 34×74=2516
练习：54×54= 83×23= 71×31= 44×64= 16×96=
4、第一个乘数互补，另一个乘数数字相同。

口诀：一个头加１后，头乘头，尾乘尾
例：37×44=？解：3＋1=4 4×4=16 7×4=28 37×44=1628
练习：37×22= 64×33= 19×88= 82×77= 73×55=
5、几十一乘几十一。

口诀：头乘头，头加头，尾乘尾。

例：21×41=？解：2×4=8 2＋4=6 1×1=1 21×41=861
练习：31×41= 61×21= 41×51= 51×71= 81×91=
作业：
加减法的巧算。

(靠整法、凑整法、分组法、基准数法)
799999＋79999＋7999＋799＋79＋7 526－73－27－26 4253－(253－158)
乘除法的巧算。

(整数乘积、乘法分配律、合理拆数、商不变性质)
练习1：25⨯32⨯125 125⨯13⨯4⨯8⨯25⨯5⨯2 456⨯2⨯125⨯25⨯5⨯4⨯8 25⨯104 125⨯88 67×101 21÷9＋22÷9＋23÷9＋24÷9 练习2：15×12= 18×12= 13×16= 18×15= 11×19=
练习3：32×38= 81×89= 53×57= 22×28= 73×77=
练习4：34×74= 82×22= 61×41= 44×64= 76×36= 练习5：37×33= 64×22= 19×55= 82×66= 73×44= 练习6：41×51= 71×81= 31×61= 21×71= 51×31=
Lesson 1 A Puma at large
逃遁的美洲狮
Listen to the tape then answer the question below.
听录音，然后回答以下问题。

Where must the puma have come from?
Pumas are large, cat-like animals which are found in America. When reports came into London Zoo that a wild puma had been spotted 45 miles south of London, they were not taken seriously. However, as the evidence began to accumulate, experts from the Zoo felt obliged to investigate, for the descriptions given by people who claimed to have seen the puma were extraordinarily similar.
The hunt for the puma began in a small village where a woman picking blackberries saw 'a large cat' only 5 yards away from her. It immediately ran away when she saw it, and experts confirmed that a puma will not attack a human being unless it is cornered. The search proved difficult, for the puma was often observed at one place in the morning and at another place 20 miles away in the evening. Wherever it went, it left behind it a trail of dead deer and small animals like rabbits. Paw prints were seen in a number of places and puma fur was found clinging to bushes. Several people complained of 'cat-like noises' at night and a businessman on a fishing trip saw the puma up a tree. The experts were now fully convinced that the animal was a puma, but where had it come from? As no pumas had been reported missing from any zoo in the country, this one must have been in the possession of a private collector and somehow managed to escape. The hunt went on for several weeks, but the puma was not caught. It is disturbing to think that a dangerous wild animal is still at large in the quiet countryside.
参考译文：。