Page 31 - 新思维数学学生用书8 样章

2 Expressions, formulae and equations

3 a Jake thinks of a number, n. Tip

Write an expression for the number Jake gets when he:
i multiplies the number by 6, then adds 1 Remember the
ii divides the number by 4, then adds 5 order of operations:
iii multiplies the number by 2, then subtracts 3 Brackets,
iv divides the number by 10, then subtracts 7. Indices,

b Jake thinks of the number 20. Work out the Division or
numbers he gets in Question 3a, parts i to iv.
Multiplication,
Addition or

Subtraction
4 Match each description with the correct expression.
The first one has been done for you: a and iv.
a Multiply n by 5 and subtract 4 b Add 4 and n, then multiply by 5
c Multiply n by 5 and add 4 d Add 5 and n, then multiply by 4

e Subtract 4 from n, then multiply by 5 f Subtract 5 from n, then multiply by 4
i 5(n + 4) ii 4(n + 5) iii 4(n − 5) iv 5n − 4
v 5n + 4 vi 5(4 − n) vii 5(n − 4)

Write a description for the expression that has not been matched.

Think like a mathematician

5 In pairs or in a small group, discuss.

Sofia and Zara discuss what to write for this problem.
‘I think of a number, n. I halve the number then add 4.’

I think the I think the
n
expression is + 4 n + 4
2 expression is
2

What do you think?
Make a conjecture and convince the other members of your group.

6 Kia thinks of a number, x.
Write an expression for the number Kia gets when she:

a divides the number by 3, then adds 1
b adds 1 to the number, then divides by 3
c subtracts 1 from the number, then divides by 3

d divides the number by 3, then subtracts 1.
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