ANSWER KEYS - Teacher Use Only

Slope-Intercept Form | Grade 8

Student Concept Worksheet Answers
1
m = 3
(17-5)/(6-2) = 12/4 = 3
2
m = -4, b = 7
In y = -4x + 7: slope is -4, y-intercept is 7
3
y = 5x - 2
Plug m = 5 and b = -2 into y = mx + b
4
y = -2x + 6
b = 6, m = (0-6)/(3-0) = -6/3 = -2
Practice Worksheet Answers

Part A: Find the Slope

#AnswerWork
1m = 2(11-3)/(5-1) = 8/4 = 2
2m = -1(4-8)/(6-2) = -4/4 = -1
3m = 0(2-2)/(3-(-3)) = 0/6 = 0 (horizontal)
4m = 3(7-(-5))/(4-0) = 12/4 = 3

Part B: Identify m and b

#Equationmb
5y = 3x + 535
6y = -2x + 8-28
7y = x - 41-4
8y = -70-7

Part C: Write the Equation

#Answer
9y = 4x - 1
10y = -3x + 6
11y = (1/2)x or y = 0.5x
12y = 5

Part D: From Tables

13
m = 2, y = 2x + 1
(5-1)/(2-0) = 4/2 = 2, b = 1
14
m = -2, y = -2x + 12
(6-10)/(3-1) = -4/2 = -2, b = 12

Part E: Real-World

15
y = 30x + 25
Slope = $30/month, Y-int = $25 joining fee
16
y = -2x + 12
Slope = -2 inches/hour (negative = decreasing), Y-int = 12 (starting height)
17
y = 2.50x + 4, Cost = $29
y = 2.50(10) + 4 = 25 + 4 = $29
18
Parallel lines (same slope, different y-intercepts)
19
y = 3x + 1
m = (13-7)/(4-2) = 6/2 = 3. Use (2,7): 7 = 3(2) + b → b = 1
FAST Practice Quiz Answers
1
B) 3
(17-5)/(6-2) = 12/4 = 3
2
B) slope = -5, y-intercept = 8
3
B) y = 2x - 3
4
Select: Positive slope, Passes through (0,2), When x=1 y=6
Positive slope (4>0) ✓
Passes through (0,2) - that's the y-intercept ✓
Goes down - NO, positive slope goes UP ✗
y=4(1)+2=6 ✓
5
B) y = 0.10x + 20
0.10 per text times x texts, plus $20 base
6
A) 11
y = 3x - 4: y = 3(5) - 4 = 15 - 4 = 11
Scoring Guide
ScoreInterpretationAction
6/6MasteryReady for systems of equations and linear modeling
4-5/6ApproachingReview specific weak area (slope calculation or interpretation)
2-3/6DevelopingReteach rise/run with visual aids. Practice identifying m and b
0-1/6InterventionStart with graphing points, then connect to slope concept
FAST Success Kit | Grade 8 | FL B.E.S.T. Standards: MA.8.AR.3.1-3.4 | Answer Key - Teacher Use Only