Page 34 - 新思维数学学生用书7 样章

2.1 Constructing expressions

Continued

Answer

Mathew is x years old. This is the information you have to start with.
David is x + 4 years old. David is 4 years older than Mathew, so add 4 to x.
Adam is x − 2 years old. Adam is 2 years younger than Mathew, so subtract 2 from x.

Kathryn is 3x years old. Kathryn is 3 times Mathew’s age so multiply 3 by x.
You write 3 × x as 3x. Always write the number before the letter.

x
Ella is years old. Ella is half Mathew’s age. You need to divide x by 2.
2 x
You write x ÷ 2 as .
2

Exercise 2.1

1 Sofia has a bag that contains n counters.
Write an expression for the total number of counters she has in the bag when:
a she puts in two more counters
b she takes out three counters.

Think like a mathematician

2 Discuss in pairs or groups.
Zara uses the following First, I said that

method to answer Sofia has 10 counters
Question 1. instead of n. For part a I need
a What do you think to work out 10 + 2. For part b I
need to work out 10 – 3. Then
of Zara’s method? I replace the 10 with n, so part

b Do you think that a becomes n + 2 and part b
this method will help becomes n – 3.
you write expressions?
c Can you improve her method?

3 The temperature on Tuesday was t °C. Tip
Write an expression for the temperature when it is:
a 2 °C higher than it was on Tuesday Twice means × 2.

b twice as warm as it was on Tuesday Half means ÷ 2.
c half as warm as it was on Tuesday

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