# 5th Grade - Using Variables In Algebra

 Grade Level: 5th Skill: Algebra Topic: Using Variables in Algebra Goal: Use a letter to represent an unknown number; write and evaluate simple algebraic expressions in one variable by substitution. Skill Description: The ability to define a variable (a letter or symbol used to represent a number) The ability to replace a variable with a number and perform the given operation. The ability to write an expression that would lead to correctly solving the problem.

### Sample Problems

 (1) Directions: Write an equation, solve and write what the variable represents. Sam had 10 pennies. He gave some away and now has 4. How many did Sam give away? ( 10 – p = 4 p stands for pennies p=6) (2) Directions: Write an equation, solve and write what the variable represents. Tim had 17 pencils. He bought some more at the store. Now he has 24 pencils. ( 17+p=24 p=7) (3) Solve for n. 23 + n= 41 ( n=18) (4) Which of the numbers 5, 6, or 7 is the solution of the equation? 49/n=7 n= x ( n = 7) (5) Evaluate the expression for each value of n. 216/n n= 3, 4, 9 ( n = 72, 54 , 24)

### Learning Tips

(1)

Math Vocabulary:

Variable- a letter or symbol that stands for a number

Equation- an algebraic or numerical sentence that shows two quantities are equal.

Expression- combines numbers or variables with operations, but has no equal sign.

(2)

Have your child practice understanding what is meant by a variable. For example you can ask your child to give certain objects around the home a variable. “What letter can we use to represent the table if we were making up a word problem?” Your child will most likely say t because table starts with the letter t. If your child says a different letter, that is fine too. Just inform your child that a variable can be any lower case letter. Explain that the most common letters used as variables are x and n.

Give them many opportunities to fully grasp the idea of a variable. Without this knowledge your child will have a very difficult time with this standard.

(3)

Have your child review key words that determine the operation to be used for word problems. Once your child knows these key words, they will have a much easier time solving all equations and word problems.

 Addition increased bymore thancombined, togethertotal ofsumadded to Subtraction decreased byminus, lessdifference between/ofless than, fewer than Multiplication oftimes, multiplied byproduct ofincreased/decreased by a  factor of (this type can  involve both addition or  subtraction and  multiplication!) Division per, aout ofratio of, quotient ofpercent (divide by 100) Equals is, are, was, were, will begives, yieldssold for

(4)

Make sure your child understands what it means to replace the variable with a given number. To help your child better understand this concept use cookies to represent the given equation. (Actually use cookies to “act out” this problem.) If you have four cookies, then you have 4 c. Some children are visual and/or kinesthetic learners so this small act will make everything connect for them.

When this concept is understood, they should be able to evaluate the following, if n = 2 17-n ( 17 – 2 =15)

(5)

When your child is having difficulties with writing expressions or equations remind them to use variables for numbers they do not know.

For example, Peter had 10 shirts. After his birthday party, he had 16 shirts. How many shirts did he receive for his birthday?

Shirts he has plus shirts received = total shirts

10 shirts + shirts received = total

10 + n = 16 n=6

10 + 6 = 16