~ 5.7 ~
Adding and Subtracting to Solve Problems
Learning Targets
I can solve problems that involve adding and subtracting rational numbers.
Notes
Sometimes we use positive and negative numbers to represent quantities in context. Here are some contexts we have studied that can be represented with positive and negative numbers:
temperature
elevation
inventory
an account balance
electricity flowing in and flowing out
In these situations, using positive and negative numbers, and operations on positive and negative numbers, helps us understand and analyze them. To solve problems in these situations, we just have to understand what it means when the quantity is positive, when it is negative, and what it means to add and subtract them.
When two points in the coordinate plane lie on a horizontal line, you can find the distance between them by subtracting their x-coordinates.
When two points in the coordinate plane lie on a vertical line, you can find the distance between them by subtracting their y-coordinates.
Remember: the distance between two numbers is independent of the order, but the difference depends on the order.
Activities
7.2 Phone Inventory
A store tracks the number of cell phones it has in stock and how many phones it sells. The table shows the inventory for one phone model at the beginning of each day last week. The inventory changes when they sell phones or get shipments of phones into the store.
What do you think it means when the change is positive? Negative?
What do you think it means when the inventory is positive? Negative?
Based on the information in the table, what do you think the inventory will be at on Saturday morning? Explain your reasoning.
What is the difference between the greatest inventory and the least inventory?
Add To Your Notes
We often use positive and negative numbers to represent changes in a quantity.
Typically…
An increase in the amount is positive.
A decrease in the quantity is negative.
7.3 Solar Power
Han's family got a solar panel. Each month they get a credit to their account for the electricity that is generated by the solar panel. The credit they receive varies based on how sunny it is!
In January they used $83.56 worth of electricity and generated $6.75 worth of electricity. Here is their electricity bill from January.
Current charges: $83.56
Solar Credit: -$6.75
Amount due: $76.81
In July they were traveling away from home and only used $19.24 worth of electricity. Their solar panel generated $22.75 worth of electricity. What was their amount due in July?
The table shows the value of the electricity they used and the value of the electricity they generated each week for a month. What amount is due for this month?
What is the difference between the value of the electricity generated in week 1 and week 2? Between week 2 and week 3?
Summary
Assignment
Check Google Classroom!