Page 71 - Math Smart - 7

For Questions 4 to 1, write down an equation. Then solve the equation.
O Mary thinks of a number and adds 5. The answer is 14.
What is the number?
O John thinks of a number and multiplies it by 6. The answer is 42.

What is the number?
O Amina thinks of a number and subtracts 14. The answer is 18.
What is the number?
O Steven thinks of a number and divides by 8. The answer is 12.

What is the number?

3.4.3 Solving equations with two

operations

In this section, you will learn to solve equations that involve two operations.

Example 3

Solve each of the following equations. Then check your answers.

O 2;c + 5 = n Solution

2x + 5 = 11
2x+ 5- 5 = 11-5 Subtract 5 from both sides of the equation / LHS = (2 X 3) +
5
2:t = 6
= 6 + 5
h =A = 11
2 2
x = 3
O £^ = Solution
3
3
=
^
4
4x(lzl)=4x3 Multiply both sides of the equation by 4
4
17-5
x-5 = ^2 / LHS =
;c-5 + 5 = 12 + 5 Add 5 to both sides of the equation 12
= 4
x = 17
= 3
O 17-5a: = 7 Solution
17-5x = 7
17 - 5;*: + 5x = 7 + 5a: Make x positive by adding 5a: to
^ both sides of the equation
17 = 7+ 5a:
17-7 = 7 +5a:- 7 Subtract 7 from both sides of the equation
10 = 5x
/ LHS = 17-{5 X 2)
Y = ^ Divide both sides of the equation by 5
= 17-10
x = 2 = 7

o