Measured 18 kg, actual 16 kg, percent error Step by Step

Step by step

The question

Question: what is the percent error, if the measurement is 18 kg and the actual value is 16 kg?

measured 18 kg, actual 16 kg

Percent error says how far off a guess is, as a percent of the real value.

error = how far off

1 Find the error

First: how far off is it?

The bigger one minus the smaller one.

18 minus 16 is 2.

The error is never negative: it is a distance.

= error = 18 − 16 = 2

2 Compare with the actual

Now we compare the error with the real value.

The error, 2, goes on top.

The actual value, 16, goes at the bottom.

= 216

erroractual

Careful!

We divide by the actual value, 16.

Not by the guess.

The real value is what we compare with.

Careful: not 218 = 11.1% ✗

3 Write it as a percent

Percent means out of 100.

16 does not go into 100.

100% is all of it: 1 whole.

Times 1 does not change the size.

So we multiply by 100%.

= 2 × 10016%

200 divided by 16 is 12.5.

200 ÷ 16 = 12.5

So it is 12.5%.

= 12.5%

So the percent error is 12.5%.

The measurement was 12.5% too high.

4 Check

Let's check: 12.5% of the actual value should give the error.

12.5% is 0.125.

0.125 times 16 is 2.

12.5% of 16 = 0.125 × 16 = 2

That is the error, 2.

So the answer is right!

Let's look back.

First: find the error.

Then: compare with the actual.

Then: write it as a percent.

Last: check.

Answer