Lesson 17Modeling with Inequalities
Learning Goal
Let’s look at solutions to inequalities.
Learning Targets
I can use what I know about inequalities to solve real-world problems.
Lesson Terms
- solution to an inequality
Warm Up: Possible Values
Problem 1
The stage manager of the school musical is trying to figure out how many sandwiches he can order with the $83 he collected from the cast and crew. Sandwiches cost $5.99 each, so he lets
Which of these are valid statements about this situation? (Select all that apply.)
He can call the sandwich shop and order exactly 13.86 sandwiches.
He can round up and order 14 sandwiches.
He can order 12 sandwiches.
He can order 9.5 sandwiches.
He can order 2 sandwiches.
He can order -4 sandwiches.
Activity 1: Elevator
Problem 1
A mover is loading an elevator with many identical 48-pound boxes.
The mover weighs 185 pounds. The elevator can carry at most 2000 pounds.
Write an inequality that says that the mover will not overload the elevator on a particular ride. Check your inequality with your partner.
Solve your inequality and explain what the solution means.
Graph the solution to your inequality on a number line.
If the mover asked, “How many boxes can I load on this elevator at a time?” what would you tell them?
Activity 2: Giving Advice
Problem 1
Your teacher will give you either a problem card or a data card. Do not show or read your card to your partner.
If your teacher gives you the problem card:
Silently read your card and think about what information you need to be able to answer the question.
Ask your partner for the specific information that you need.
Explain how you are using the information to solve the problem.
Continue to ask questions until you have enough information to solve the problem.
Share the problem card and solve the problem independently.
Read the data card and discuss your reasoning.
If your teacher gives you the data card:
Silently read your card.
Ask your partner “What specific information do you need?” and wait for them to ask for information.
If your partner asks for information that is not on the card, do not do the calculations for them. Tell them you don’t have that information.
Before sharing the information, ask “Why do you need that information?”
Listen to your partner’s reasoning and ask clarifying questions.
Read the problem card and solve the problem independently.
Share the data card and discuss your reasoning.
Pause here so your teacher can review your work. Ask your teacher for a new set of cards and repeat the activity, trading roles with your partner.
Are you ready for more?
Problem 1
In a day care group, nine babies are five months old and 12 babies are seven months old. How many full months from now will the average age of the 21 babies first surpass 20 months old?
Lesson Summary
We can represent and solve many real-world problems with inequalities. Whenever we write an inequality, it is important to decide what quantity we are representing with a variable. After we make that decision, we can connect the quantities in the situation to write an expression, and finally, the whole inequality.
As we are solving the inequality or equation to answer a question, it is important to keep the meaning of each quantity in mind. This helps us to decide if the final answer makes sense in the context of the situation.
For example: Han has