SME
Grade 7 Math · Problem type
Percent error
Use this for “A kitchen scale reads 245 g for a 250 g weight. What is the percent error?”
Diagram
2% of 250 is 5.
m = 245 (measured value)
This is an example. Type your own values to start a new problem.
|
m
−
t
|
=
e
e
÷
t
×
100
=
p
%
Formulas
e
=
|
m
−
t
|
(error
=
|measured
value
−
actual
value|)
5 = |245 − 250|
p
=
e
÷
t
×
100
(percent
error
=
error
÷
actual
value
×
100)
2 = 5 ÷ 250 × 100
Assumptions
•
The error is the gap between the measured value and the actual value, never negative.
•
Percent error = error ÷ actual value × 100: divide by the actual value, not the measured one.
•
A small percent error means a good measurement.
Step-by-step
WE KNOW
t = 250 (actual value), m = 245 (measured value)
FIND
error (e), percent error (p)
Step 1 · Find error (e)
Use e = |m − t| (error = |measured value − actual value|)
The gap between the measured and the actual value.
e
=
|245
−
250|
e
=
|−5|
e
=
5
Step 2 · Find percent error (p)
Use p = e ÷ t × 100 (percent error = error ÷ actual value × 100)
Divide the error by the actual value, then × 100.
p
=
5
250
×
100
p
=
0.02
×
100
p
=
2%
Check
Put the numbers back in. Both sides should match.
5 = 250 − 245 ✓
2 = 5 ÷ 250 × 100 ✓
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