Slippery SlopesA lesson on interpreting slope and y-intercept

in real world examples

Standard:MAFS.912.S-ID.3.7:

Interpret the slope (rate of change) and the intercept (constant term) of a linear model in the context of the data.

Problem of the Day:

Solve for the slope between (-1,-5) and (6,9).

m=2

m= y2-y1 x2-x1

m= 9-(-5) 6-(-1)

m= 14 7

VocabularySlope intercept form- y=mx+b, where m is slope and b is the y-intercept

Slope- Change in y over change in x (rate of change)

Y-intercept- the value of y when x is zero

Example of Slope in a Real World Scenario

m= Change in height Change in time

The graph to the right shows the growth of a tree at a constant rate, over a period of four years. Interpret the slope of the line.

Example of Slope in a Real World Scenario

m= change in distance change in time

Click icon to add picture

Example of Y-Intercept in a Real World Scenario.

For example: The y-intercept in this graph is 1080, meaning it is the amount the person owes before he/she begins making payments (zero payments have been made, $1,080 owed).

The graph then shows that over the next 24 months this debt will be paid off.

Example of Y-Intercept in a Real World Scenario

You have 300 items of clothing and decide to start donating to Goodwill. Your y-intercept is the amount of clothing you have before you start donating to Goodwill every month.

Solving a Real World ExampleA student is eating an ice

cream cone at the park that is 12.7cm tall. It is extremely hot outside and the ice cream starts to melt at a constant rate of 2cm/minute. If the student didn’t eat any of the ice cream and it started to melt, how much would be left after 3 minutes?

1st: Identify the slope and y-intercept

2nd: Plug into slope intercept formY=-2x+12.7 (slope is

negative because it is decreasing in size)

3rd: Plug in 3 for x since we want to know how tall it will be after 3 minutes

4th: Solvey=-2(3)+12.7y=-6+12.7y=6.7

Understand that after 3 minutes of melting the ice cream cone will now measure 6.7cm.

Leaky Lines ProjectItems you should

have:400ml of water500ml+ graduated

cylinderEmpty water bottleStopwatch

Leaky Lines ProjectGet into groups of

twoOne person will hold

the water bottle and be in charge of the stopwatch

Measure 400ml into bottle

Turn water bottle over and start timer

Every 10 seconds record how much water has accumulated in the cylinder

Leaky Lines ProjectCreate a graph based

on the data gathered graphing the time intervals on the x-axis and the amount of milliliters on the y-axis.

Solve for the rate of change between two coordinates.

Write the equation of the line.

Discussion:Is the slope positive

or negative?What is the y-

intercept?

Independent PracticeHad we been

measuring the rate at which the water left the bottle, would the slope have been positive or negative?

What would the y-intercept have been?

Write an equation expressing this linear relationship using m for slope.

Review for Quiz1. Your family is taking a trip to Disney and is

driving at a constant rate. After one hour, you have traveled 60 miles, and after 2 hours you have traveled 120 miles. How fast is the car going?

2. You are selling candy bars for a fundraiser. You have raised $50 so far and sell each candy bar for 75 cents. How much money will you have made after selling 30 candy bars?

Review for Quiz ContinuedThe graph shows the

amount of money you have at the beginning of the month.

a. How much money did you begin with? b. How much money do you earn each week? c. How much money will you have after 3 weeks?