Question 1
Part A: Identify Changes at a Constant Rate
- Number of Bacteria: The amount of bacteria doubles every hour. This is exponential growth, not a constant rate.
- Population of a City: Growing at a rate of 2% each year. This is also exponential growth, not a constant rate.
- Distance Traveled by a Car: If the car travels at a constant speed of 60 miles per hour, the distance changes at a constant rate (60 miles for each hour).
- Money Earned: Earning $15.75 per hour shows a linear relationship; it changes at a constant rate based on time.
Conclusion: The distance traveled by a car going 60 miles per hour and the amount of money earned at $15.75 per hour both represent quantities that change at a constant rate.
Part B: Mathematical Equation
For the distance traveled by a car at 60 mph:
- Distance (D) = 60 * Time (T)
For the amount of money earned:
- Money (M) = 15.75 * Time (T)
Real-World Problem
If someone works for \( T = 5 \) hours at $15.75 per hour:
- Money earned \( M = 15.75 * 5 = 78.75 \)
Predictions About Future Values: Using \( M = 15.75 * T \), one can predict future earnings based on hours worked.
Limitations: This model assumes constant pay and hours without breaks, taxes, or changes in pay rate.
Question 2
Part A: Independent and Dependent Variables
-
Insects increasing by 2% per week:
- Independent: Time (weeks)
- Dependent: Number of insects
- Dependent variable grows by a constant percent.
-
School population increasing by 100 students per year:
- Independent: Time (years)
- Dependent: Population of the school
- Grows by a constant amount.
-
Money in a savings account with 5% compound interest:
- Independent: Time (years)
- Dependent: Amount of money in the account
- Grows by a constant percent.
-
Value of a house increasing by 3% a year:
- Independent: Time (years)
- Dependent: Value of the house
- Grows by a constant percent.
-
Fuel used by a car (32 mpg):
- Independent: Distance traveled
- Dependent: Amount of fuel used
- Grows linearly, not by percent.
Situation that Grows by Constant Percent: Money in a savings account.
Equation to Model This Situation
Using the compound interest formula:
\[ A = P(1 + r)^t \]
Where:
- \( A \): Amount of money after \( t \) years
- \( P \): Principal amount (initial deposit)
- \( r \): interest rate (5% = 0.05)
- \( t \): time in years
Part C: Table of Values
| Year (t) | Amount (A) | |----------|---------------------------------| | 0 | P | | 1 | P(1 + 0.05) = 1.05P | | 2 | P(1 + 0.05)² = 1.1025P | | 3 | P(1 + 0.05)³ = 1.157625P | | 4 | P(1 + 0.05)⁴ = 1.21550625P |
Part D: Graphing
Plot the values from the table to see the exponential growth over time.
Question 3
Concept of Decay by Constant Percent Rate
Decay by a constant percent rate per unit interval refers to a situation where a quantity consistently decreases by a specific percentage with each time interval.
- Key Terms:
- Initial Value: The starting point of the quantity.
- Decay Rate: The percentage by which the quantity decreases in each interval.
- Unit Interval: The interval over which the decay occurs (e.g., time, distance).
Example: A car depreciating in value by 15% each year.
Part B: Real-World Scenario
Car Depreciation: A car valued at $20,000 depreciates at 15% annually. This decrease in value represents an important financial consideration for buyers and sellers in the used car market.
Part C: Exponential Decay Equation
Let \( C \) be the value of the car. We can express this as:
\[ C(t) = C_0(1 - r)^t \]
where:
- \( C_0 \): Initial value ($20,000)
- \( r \): Decay rate (15% = 0.15)
- \( t \): Time in years
The equation becomes:
\[ C(t) = 20000(1 - 0.15)^t \]
or
\[ C(t) = 20000(0.85)^t \]
Part D: Table
| Year (t) | Value (C) | |----------|-------------------| | 0 | $20,000 | | 1 | $20,000(0.85) = 17,000 | | 2 | $20,000(0.85)² = 14,450 | | 3 | $20,000(0.85)³ = 12,282.5 | | 4 | $20,000(0.85)⁴ = 10,453.125 |
Part E: Graphing
Graph the remaining value of the car over time. It illustrates exponential decay.
Question 4
Part A: Analyze Graph
- Y-Intercept: The y-value when x = 0.
- Slope: The change in y for a given change in x.
Part B: Equation
The linear equation can be written as:
\[ y = mx + b \]
where \( m \) is the slope and \( b \) is the y-intercept.
Part C: Real-World Situation
Example: Total cost of buying 3 bottles of water at $2.50 each.
Part D: Making a Prediction
Using the graph, if 3 bottles are bought, the total cost can be calculated or predicted based on the slope/intercept.
Question 5
Linear Relationships
- Distance Car Travels:
- Quantities: Distance and Time.
- Cost of Water:
- Quantities: Total Cost and Number of Bottles.
- Area of Rectangle:
- Quantities: Length and Width.
- Volume of Prism:
- Quantities: Length, Width, Height.
Chosen Situation: Total cost of buying bottles of water.
Part B: Equation
The linear relationship can be modeled as:
\[ C = 2.50b + 20 \]
where \( C \) is the cost and \( b \) is the number of bottles.
Meaning:
- Slope ($2.50) is the cost per bottle.
- Y-Intercept ($20) is a fixed cost (e.g., water jug).
Part C: Values Table
| Number of Bottles (b) | Total Cost (C) | |------------------------|-------------------------| | 0 | $20 | | 1 | $22.50 | | 2 | $25 | | 3 | $27.50 |
Graph the values to represent the linear relationship visually.