SME
Grade 8 Math · Statistics & Probability
Scatter plots and lines of fit
Use this for “The line of fit is y = 2.5x + 2. Predict the points scored after 4 hours of practice.”
Chart
Line of fit: y = 2.5x + 2
7 points above the line, 7 below.
Prediction for x of 4: y = 2.5 × 4 + 2 = 12
The outlier (1, 26) sits far from the rest.
This is an example. Type your own values to start a new problem.
y
=
m
×
x
+
b
Formulas
y
=
m
×
x
+
b
(predicted
points
=
slope
×
hours
of
practice
+
intercept)
12 = 2.5 × 4 + 2
Assumptions
•
Each dot is one player: hours of practice a week and points scored in a game.
•
A line of fit follows the trend, with about as many dots above it as below.
•
The slope says how many more points for each extra hour; the intercept is the prediction at 0 hours.
•
One dot far from the rest is an outlier; a bunch close together is a cluster.
Step-by-step
WE KNOW
m = 2.5 (slope), b = 2 (intercept), x = 4 (hours of practice)
FIND
predicted points (y)
Step 1 · Find predicted points (y)
Use y = m × x + b (predicted points = slope × hours of practice + intercept)
Read
the
line:
slope
times
the
input,
plus
b
.
y
=
2.5
×
4
+
2
y
=
10
+
2
y
=
12
Check
Put the numbers back in. Both sides should match.
12 = 2.5 × 4 + 2 ✓
Topic check
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