Montana Math MT.8.F.4

Math8th GradeFunctions

The Standard

Given linear data relating two quantities, construct a linear function that models the data and interpret the rate of change and initial value of a linear function in terms of the situation it models.

2026 Montana Mathematics Content Standards

Teacher's field guide

What This Standard Means

What Students Need to Do

Students use data from a table or graph to write a linear rule. They find the change in output for each one-unit increase in input. They explain that rate and the value at zero using the units in the problem.

What Mastery Looks Like

Given rental costs of $11 for 1 hour and $21 for 3 hours, a student writes C = 5h + 6. They explain that each hour adds $5 and the rental starts with a $6 fee.

Common Misconceptions

Students may subtract two costs but forget to divide by the change in hours. They may call the first cost in a table the starting fee, even when the table begins at 1 hour. Some reverse the input and output when finding the rate.

How to Assess It

Exit ticket: A scooter rental costs $14 for 2 hours and $26 for 5 hours. Write a cost rule in terms of hours, then state the hourly rate and starting fee.

Lesson moves

Ways to Teach It

  1. Use counters to model a $4 taxi fee plus $2 per mile for 0 to 4 miles; record totals and write the rule.

  2. Show rental costs of $11 for 1 hour and $21 for 3 hours; ask what the hourly rate and starting fee mean.

  3. Give pairs three cost tables; partners race to write a rule for each and label the rate with its units.

  4. Post a sample parking sign: $3 to enter, plus $2 per hour; have students calculate three charges and explain both fees.

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Printable MT.8.F.4 Worksheet

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