第一单元

Unit 1

Today I'm in charge -- multiplication by decimals

一 今天我当家 ——小数乘法

Lesson 1

Hurry up ！

快点啊!

Mother said to turn off the light before going out.

妈妈说，出门前要关灯。

What questions can you ask?

你能提出什么问题？

Cooperative exploration

合作探索

1. How much is the water charge for August?

1. 8月份的水费是多少钱？

Two point eight times four equals to ______(yuan )

2.8×4＝________(元)

A factor is a decimal. How do you compute it?

一个因数是小数，怎样计算？

You can just do it with vertical form.

可以直接用竖式计算。

How much is the electricity charge in August?

2. 8月份的电费是多少钱？

Zero point five times fifty-one equals to _______(yuan)

0.5×51＝________(元)

Would you calculate 0.55×64?

你会计算0.55×64吗？

Think about it. How do you multiply a decimal by an integer?

想一想，怎样计算小数乘整数？

Lesson 2

Meat: 25.6 yuan /kg          Fish: 14.8 yuan /kg

肉：25.6元//kg              鱼：14.8元/kg

I bought 0.9 kilograms of meat and 1.5 kilograms of fish.

买了0.9千克肉和1.5千克鱼。

What questions can you ask?

你能提出什么问题？

Cooperative exploration

合作探索

How much did you pay for the meat?

1. 买肉花了多少钱？

Twenty-five point six times zero point nine equals to _____(yuan)

25.6×0.9＝_________(元)

It can be converted to integer multiplication.

可以转化成整数乘法计算。

Work out the product by integer multiplication and add the decimal point to the total point.

先按整数乘法算出积，再给积点上小数点。

You can see how many decimal places there are in the factor, you start with the right-hand side of the product and you add the decimal point.

可以看因数中一共有几位小数，就从积的右边起数出几位，点上小数点。

2. How much did the fish cost?

2. 买鱼花了多少钱？

Would you calculate 0.48×0.06?

你会计算0.48×0.06吗？

What if I don't have enough decimal places?

积的小数位数不够怎么办？

I want to fill in the zeros in front, and then dot the decimal point.

要在前面用0补足数位，再点小数点。

Think about it. How do you multiply decimals?

想一想，怎样计算小数乘法？

Lesson 3

Soybeans: 4.82 yuan/kg

黄豆：4.82元/千克

Mung beans

绿豆： ?

Rice: 4.72 yuan/kg

大米 ：4.72元/千克

Millet : 5.28 yuan/kg

小米5.28元/千克

The unit price of mung beans is 1.5 times that of soybeans.

绿豆的单价是黄豆的1.5 倍。

I buy 2.5 kilos of mung beans......

我买2.5千克绿豆......

What questions can you ask?

你能提出什么问题？

Cooperative exploration

合作探索

1. How much does it cost to buy 2.5 kilos of mung beans?

1. 买2.5 千克绿豆需要多少钱？

I calculate the price per kilogram of mung beans and then how much it would cost to buy 2.5 kilograms.

我先算每千克绿豆的价钱，再算买2.5千克需要多少钱。

2. If I buy 2.5 kilos of rice and 2.5 kilos of millet, how much will it cost altogether?

2. 如果大米、小米各买2.5千克，一共需要多少钱？

I found that the distributive property of integer multiplication also holds true for decimal multiplication.

我发现，整数乘法的分配律对小数乘法同样适用。

Do the other laws of integer multiplication apply to decimal multiplication?整数乘法的其他运算律对小数乘法适用吗？