第二单元

Unit two

Energy conservation and emission reduction -- use letters for numbers

节能减排——用字母表示数

Lesson One

第一课

A water-saving faucet can save 10 milliliters of water per minute.

一个节水水龙头每分钟可节水10毫升。

You can save electricity by turning off electrical appliances when you go out.

出门时关闭电器开关可以节约用电。

What questions can you ask?

你能提出什么问题？

Water-saving faucet 2 minutes Water-saving how many milliliters? Three minutes, four minutes......

1. 节水水龙头2分钟节水多少毫升？3分钟、4分钟......

Can you simply write a formula for how much water you save at any given time?

你能用一个式子简单地表示出任何时间的节水量吗？

In mathematics, we often use letters to represent numbers.

在数学中，我们经常用字母来表示数。

Time is usually represented by letters, and the amount of water saved in t minutes is represented as 10×t

通常用字母表示时间，t分钟的节水量表示为10×t

Xiao Ming used to pay m yuan for electricity every year, but now he can save 150 yuan for electricity every year.

2. 小明家原来每年的电费是m元，现在每年节省电费150元。

3. What is the annual electricity cost after saving electricity

3. 节约用电后每年的电费是多少元？

When m=900, what is the current annual electricity cost?

当m=900时，现在每年的电费是多少元？

m-150

=900-150

=750

A: The current electricity bill is 750 yuan a year.

答：现在每年的电费是750元。

Lesson two

第二课

Electric cars travel 60 kilometers per hour

电动汽车每小时行驶60千米。

What questions can you ask?

你能提出什么问题？

How to express the relationship between the speed, time and distance of a car in a formula containing letters?

怎样用一个含有字母的式子表示汽车行驶速度，时间和路程之间的关系？

It's usually S for distance, V for speed, and T for time.

通常用S表示路程V表示速度，T表示时间。

 S=V×T

If T is equal to 3, how many kilometers did the electric car travel?

如果T等于3，电动汽车行驶了多少千米？

 S=V×t

=60×3

=180

A: The electric car travels 180 kilometers in three hours.

答：电动汽车三小时行驶了180千米。

If the perimeter is represented by C and the area is represented by S, can you write out the formula for the circumference and area of a square with letters?

如果用C表示周长，用S表示面积，你能用字母表示出正方形周长和面积的计算公式吗？

 C=4×a，s=a×a。

A ×4 and 4× A are usually written as 4.A or 4A.

 a×4和4×a，通常可以写成4.a或4a。

A cross a can be rewritten as a a or it can be rewritten as a squared, which is read as a squared means two A's multiplied.

 a×a可以写成a.a也可以写成a2，读作a的平方表示2个a相乘。

Can you use letters to express the formula for calculating the circumference and area of a rectangle?

你能用字母表示长方形周长和面积的计算公式吗？