1. Skill Check
Lesson Presentation
Lesson Quiz

2. Skill Check 1. 8
–72 2. 3. 14 4.
–26

3. Biology Lotus flowers like the one shown can be grown from seeds hundreds of years old. You will see how an equation can be used to estimate the year when an ancient lotus seed was formed.

4. An equation is a mathematical sentence formed by placing an equal sign, =, between two expressions. A solution of an equation with a variable is a number that produces a true statement when it is substituted for the variable.

5. 1 Writing Verbal Sentences as Equations Verbal Sentence Equation
EXAMPLE 1
Writing Verbal Sentences as Equations
Verbal Sentence
Equation
The sum of x and 6 is 9.
x + 6 = 9

6. 1 Writing Verbal Sentences as Equations Verbal Sentence Equation
EXAMPLE 1
Writing Verbal Sentences as Equations
Verbal Sentence
Equation
The sum of x and 6 is 9.
x + 6 = 9
The difference of 12 and y is 15.
12 – y = 15

7. 1 Writing Verbal Sentences as Equations Verbal Sentence Equation
EXAMPLE 1
Writing Verbal Sentences as Equations
Verbal Sentence
Equation
The sum of x and 6 is 9.
x + 6 = 9
The difference of 12 and y is 15.
12 – y = 15
The product of –4 and p is 32.
–4p = 32

8. 1 Writing Verbal Sentences as Equations Verbal Sentence Equation
EXAMPLE 1
Writing Verbal Sentences as Equations
Verbal Sentence
Equation
The sum of x and 6 is 9.
x + 6 = 9
The difference of 12 and y is 15.
12 – y = 15
The product of –4 and p is 32.
–4p = 32
= 9 n 2
The quotient of n and 2 is 9.

9. 2 Checking Possible Solutions
EXAMPLE 2
Checking Possible Solutions
Tell whether 9 or 7 is a solution of x – 5 = 2.
Substitute 9 for x.
x – 5 = 2
9 – 5 = 2 ?
4 = 2
ANSWER
9 is not a solution.

10. 2 Checking Possible Solutions
EXAMPLE 2
Checking Possible Solutions
Tell whether 9 or 7 is a solution of x – 5 = 2.
Substitute 9 for x.
Substitute 7 for x.
x – 5 = 2
x – 5 = 2
9 – 5 = 2 ?
7 – 5 = 2 ?
4 = 2
2 = 2
ANSWER
9 is not a solution.
ANSWER
7 is a solution.

11. Solving Equations Finding all solutions of an equation is called solving the equation. You can use mental math to solve a simple equation by thinking of the equation as a question.

12. 3 Solving Equations Using Mental Math Equation Question Solution Check
EXAMPLE 3
Solving Equations Using Mental Math
Equation
Question
Solution
Check
What number plus 3 equals 11?
x + 3 = 11 8
8 + 3 = 11

13. 3 Solving Equations Using Mental Math Equation Question Solution Check
EXAMPLE 3
Solving Equations Using Mental Math
Equation
Question
Solution
Check
What number plus 3 equals 11?
x + 3 = 11 8
8 + 3 = 11
16 minus what number equals 9?
16 – m = 9 7
16 – 7 = 9

14. 3 Solving Equations Using Mental Math Equation Question Solution Check
EXAMPLE 3
Solving Equations Using Mental Math
Equation
Question
Solution
Check
What number plus 3 equals 11?
x + 3 = 11 8
8 + 3 = 11
16 minus what number equals 9?
16 – m = 9 7
16 – 7 = 9
20 equals 5 times what number?
20 = 5t 4
20 = 5(4)

15. 3 Solving Equations Using Mental Math Equation Question Solution Check
EXAMPLE 3
Solving Equations Using Mental Math
Equation
Question
Solution
Check
What number plus 3 equals 11?
x + 3 = 11 8
8 + 3 = 11
16 minus what number equals 9?
16 – m = 9 7
16 – 7 = 9
20 equals 5 times what number?
20 = 5t 4
20 = 5(4)
= –3 y 6
What number divided by 6 equals –3?
= –3
–18 6
–18

16. Age of seed when it sprouted
EXAMPLE 4
Writing and Solving an Equation
From 1998 to 2002, biologist Jane Shen-Miller grew several lotus plants from ancient seeds she found in China. The oldest seed was about 500 years old. Estimate the year when this seed was formed.
SOLUTION
First write a verbal model for this situation.
Year seed was formed
Age of seed when it sprouted
Year seed sprouted + =

17. 4 x + 500 = 2000 1500 + 500 = 2000 Writing and Solving an Equation
EXAMPLE 4
Writing and Solving an Equation
From 1998 to 2002, biologist Jane Shen-Miller grew several lotus plants from ancient seeds she found in China. The oldest seed was about 500 years old. Estimate the year when this seed was formed.
SOLUTION
Let x represent the year when the seed was formed. Because you are only trying to estimate x (rather than determine x precisely), you can use 2000 for the year when the seed sprouted. This year simplifies mental calculations and lies within the given time period, 1998–2002.
x = 2000
Substitute for quantities in verbal model.
= 2000
Use mental math to solve for x.
ANSWER
Because x = 1500, the seed was formed around the year 1500.

18. Lesson Quiz
Solve the equation using mental math.
1. a + 11 = 19 8
2. 34 – b = 27 7
3. –3c = 12 –4 4. 9
5. Challenge Solve the equation 3y – 2 = 13. 5