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8th Grade Math Prompt 1

1. Desiree deposits 1000 in her savings account.

The account pays simple interest at a rate of

5 per year. How much will be in her account

after three years? (Assume that she does not

deposit or withdraw any other amounts during

this time.)

- Make a table to follow the account.
- year in account
- 0 1000
- 1 (5 of 1000) 1000 (50)

1000 1050 - 2 (5 of 1050) 1050 (52.50)

1050 1,102.50 - 3 (5 of 1,102.50) 1,102.50

(55.13) 1,102.50 1,157.63

Answer 1,157.63

Grading was as follows

- 2 points both procedure answer correct
- 1 point correct procedure or correct answer
- 0 point no correct procedure or answer

2. A grocery store receives a shipment of 50

gallons of milk. It has 46 gallons left after

2 hours, 22 gallons left after14 hours, and 8

gallons left after 21 hours. Draw a graph of

the quantity of milk left as a function of time

and find the slope of the graph.

- First graph the data.

Milk Left

60 50 40 30 20 10

Gallons

Remember your titles and choose a correct scale!

0 10 20 30 40

50 60

Time

Find the slope by choosing two points on the

graph. Remember, slope is rise / run or the

change in y / change in x.

22 46 -24 -2 14 2 12

Milk Left

60 50 40 30 20 10

(2,46)

Gallons

(14,22)

0 10 20 30 40

50 60

Answer Slope is - 2

Time

Grading was as follows

- 2 points graph and equation were correct
- 1 point graph or equation were correct
- 0 points no correct answers

3. a. Write an equation of the line with slope 4

and y-intercept 5.

- Since the slope intercept form of a line is
- y mx b
- where m is the slope and b is the

y-intercept, we can just plug in the given values.

Answer y 4x 5

b. Write an equation of the line with slope 5

that passes through the point (0,3).

- First fill in the equation with the values you

already know. - y 5x b

You need to find the y-intercept or b. Do this

by plugging in the x and y values from the given

point. Then solve for b. 3 5(0) b 3

0 b 3 b

Answer y 5x 3

c. What is the equation of the following line?

8 6 4 2

2 4 6 8

-8 -6 -4 -2

-2 -4 -6 -8

I can see the y-intercept is 5.

I need to calculate the slope. Rise / Run or

change in y / change in x. Slope - 2

8 6 4 2

Pick two points. (0,5) and (2,1)

1 - 5 -4 -2 2 0 2

2 4 6 8

-8 -6 -4 -2

-2 -4 -6 -8

Equation of line y -2x 5

Grading was as follows

- 3 points all three answers correct
- 2 points two of three answers correct
- 1 point one of three answers correct
- 0 points no correct answers