Lesson 1.3 Variables and Expres-

sions

By Yeo Chang Yoon

Vocabulary 1

Variable: A variable is a symbol or a letter, that represent one or more numbers.

Vocabulary 2

Variable expression: It is an ex-pression that consists of numbers, variables, and operations.

How to evaluate a variable expres-sion

To evaluate a variable expression, sub-stitute a number for each variable. Then find the value of the numerical expression.

Using a Variable Expression

If a car travels 80 kilometers per hour, what is the distance the car will travel in 5 hours?

Speed X Time=80t =80(5) =400

Answer: The car will travel 400km.

Evaluating Variable Expressions

Evaluate the expression when x=10 and y=5.

1. 45x+5=45(10)+5 2. 4y+5=4(5)+5

=450+5 =20+5 =455 =25

Translating Verbal Phrases

Verbal Phrase Variable Expres-sion

The sum of a number and 2 n+2 The difference of a number and 5 n-5 The product of 10 and a number nX10 The quotient of 48 and a number 48/n One Third of a number 1/3n

Writing and Evaluating an Expres-sion

To find the average weight of a male person whose height is 150cm or over, subtract 100 from the height and multiply 0.9.

Find the average weight of a boy whose height is 160cm.

0.9(h-100)=0.9(160-100) =0.9(60) =54

Answer: The average weight of the boy is 54kg.

The end