Page 52 - 新思维数学学生用书7 样章

2.5 Constructing and solving equations

Exercise 2.5

1 Copy and complete the workings to solve these equations.
Check your answers are correct.
a x + 6 = 10 b x − 6 = 10 c 2x = 10

x + 6 − 6 = 10 − x − 6 + 6 = 10 + 2x = 10
x = x = 2
x =

2 Solve each of these equations and check your answers.
a x + 4 = 11 b x + 3 = 6 c 2 + x = 15 d 7 + x = 19
e x − 4 = 9 f x − 2 = 8 g x − 12 = 14 h x − 18 = 30
i 3x = 12 j 5x = 30 k 7x = 70 l 12x = 72
3 Dayita uses this method to solve an equation when the unknown is on the right-hand side of the

equation.

Solve the equation: 12 = y + 3

Write this as: y + 3 = 12
Solve as normal: y + 3 − 3 = 12 − 3
y = 9

Use Dayita’s method to solve these equations.
a 15 = y + 3 b 9 = y + 2 c 13 = y − 5
d 25 = y − 3 e 24 = 8y f 42 = 6y

4 Write an equation for each of the following. Then solve each
equation to find the value of the unknown number. Tip
a I think of a number and add 3. The answer is 18. In part a,
b I think of a number and subtract 4. The answer is 10. n + 3 = 18.

c I think of a number and multiply it by 4. The answer is 24.
5 Zara is considering the equation 4n = 24.
a Write an ‘I think of a number’ statement

for each of these equations.
This equation
i n – 8 = 3 could come from the
ii n + 5 = 12 statement: I think of a
iii 8n = 96 number, multiply it by 4,
b Solve the equations in part a. and the answer
is 24.

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