Writing Linear Equations

To Write an Equation:

• Decide what your are trying to find – this is the unknown

• Choose a variable to represent that unknown• Use mathematical “key words” to write an

equation

KEY WORDS

ADD SUBTRACT MULTIPLY DIVIDEsum difference product quotientadded to minus times divided bytogether subtracted multipliedtotal from ofplus less

less than discount

“Is” means EQUALS

Examples

• Jack is five years older than half the age of his sister. Jack is 13 years old. How old is his sister?

• Kathy is 3 years younger than twice the age of her brother. Kathy is 17 years old. How old is Kathy’s brother?

• The sum of 9 and the product of 4 and a number is 25. What is the number?

• The difference of three times a number and six is 28. What is the number?

Examples

• Lucy has four times as many DVDs as Erica has. Together, they have 80 DVDs. Write an equation to find out how many DVDs each girl has.

• Vanessa has 6 times as many shoes as Missy. Together they have 44 pairs of shoes. Write an equation to find how many shoes each girl has.

• A truck driver drove 450 miles yesterday. He drove 65 miles per hour before he stopped at a truck stop for lunch. After lunch he drove 190 miles. Write an equation to represent the number of hours that the driver drove before stopping for lunch.

Last Example

• Membership at the skating rink is $50 a year. If you are a member, the cost of renting skates is $3. If you budget $110 a year to go skating, write an equation to find how many times can you go.