1. EXAMPLE 5
Simplify a mathematical model
Digital Photo Printing
You send 15 digital images to a printing service that charges $.80 per print in large format and $.20 per print in small format. Write and simplify an expression that represents the total cost if n of the 15 prints are in large format. Then find the total cost if 5 of the 15 prints are in large format.

2. Simplify a mathematical model
EXAMPLE 5
Simplify a mathematical model
SOLUTION
Write a verbal model. Then write an algebraic expression.
An expression for the total cost is 0.8n + 0.2(15 – n).
0.8n + 0.2(15 – n)
= 0.8n + 3 – 0.2n
Distributive property.
= (0.8n – 0.2n) + 3
Group like terms.

3. Simplify a mathematical model
EXAMPLE 5
Simplify a mathematical model
= 0.6n + 3
Combine like terms.
ANSWER
When n = 5, the total cost is 0.6(5) + 3 = = $6.

4. GUIDED PRACTICE
for Example 5
What If? In Example 5, write and simplify an expression for the total cost if the price of a large print is $.75 and the price of a small print is $.25.
SOLUTION
Write a verbal model. Then write an algebraic expression.
0.75 n
0.25
(15 – n) +

5. An expression for the total cost is 0.75n + 0.25(15 – n).
GUIDED PRACTICE
for Example 5
An expression for the total cost is 0.75n (15 – n).
0.75n (15 – n)
= 0.75n – 0.2n
Distributive property.
= 7.5n – 0.25n
Group like terms.
= 0.5n
Combine like terms.