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## Algebra (all content)

### Course: Algebra (all content)>Unit 1

Lesson 3: Substitution and evaluating expressions

# Evaluating expressions

Learn to evaluate all sorts of expressions: expressions with one variable, two variables, fractions and decimals, and even expressions in word problems.
Evaluating expressions with two variablesSee video transcript

#### Try it yourself

Evaluate 2, c, plus, 1 when c, equals, 4.

## Let's study another example.

Evaluate 10, minus, start fraction, m, divided by, n, end fraction, plus, n when m, equals, 6 and n, equals, 3.
empty space, 10, minus, start fraction, start color #11accd, m, end color #11accd, divided by, start color #e07d10, n, end color #e07d10, end fraction, plus, start color #e07d10, n, end color #e07d10
equals, 10, minus, start fraction, start color #11accd, 6, end color #11accd, divided by, start color #e07d10, 3, end color #e07d10, end fraction, plus, start color #e07d10, 3, end color #e07d10, space, space, space, space, space, space, space, space, start text, R, e, p, l, a, c, e, space, end text, start color #11accd, m, end color #11accd, start text, space, w, i, t, h, space, end text, start color #11accd, 6, end color #11accd, start text, space, a, n, d, space, end text, start color #e07d10, n, end color #e07d10, start text, space, w, i, t, h, space, end text, start color #e07d10, 3, end color #e07d10
equals, 10, minus, 2, plus, 3
equals, 11

## Let's try some practice problems!

Evaluate 10, minus, a when a, equals, 1.

Evaluate 6, b when b, equals, 2.

Evaluate 7, c, minus, 4 when c, equals, 3.

Evaluate start fraction, 8, divided by, d, end fraction, plus, 3 when d, equals, 4.

Evaluate 6, a, ​, ​, plus, 4, b, minus, 6 when a, equals, 1 and b, equals, 3.

Evaluate 5, x, minus, start fraction, x, divided by, y, end fraction when x, equals, 4 and y, equals, 2.

Evaluate start fraction, 3, divided by, 2, end fraction, y, minus, 3, plus, start fraction, 5, divided by, 3, end fraction, z when y, equals, 4 and z, equals, 3.

Evaluate 13, minus, 0, point, 5, w, plus, 6, x when w, equals, 10 and x, equals, start fraction, 1, divided by, 2, end fraction.

## Let's try a word problem

The expression 2, m, plus, 10, c gives the amount of money (in dollars) a dessert store makes from selling m muffins and c cakes.
How much money does the dessert store make from selling 3 muffins and 4 cakes?
dollars

## Challenge problem 1

Complete the table to evaluate 2, x at different values of x.
x2, x
12
24
36
4
5
6

## Challenge problem 2

A flower store uses the expression 2, plus, 5, r to determine the cost (in dollars) of r roses.
Complete the table to find the cost of different numbers of roses.
Number of roses left parenthesis, r, right parenthesisCost left parenthesis, 2, plus, 5, r, right parenthesis
317
6
9

Cam has 32 dollars. How many roses can he afford to buy?
Assume that he wants to buy as many roses as he can.

#### Extra challenge

Explain to a family member, friend, or classmate why the cost of 6 roses is not double the cost of 3 roses.