Maya guessed 30 jelly beans. There were 25. What is the percent error?

Step by step

The question

Question: what is the percent error, if Maya guessed 30 jelly beans and there were really 25?

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

1 Find the error

First: how far off is it?

The bigger one minus the smaller one.

30 minus 25 is 5.

The error is never negative: it is a distance.

2 Compare with the actual

Now we compare the error with the real value.

The error, 5, goes on top.

The actual value, 25, goes at the bottom.

Careful!

We divide by the actual value, 25.

Not by the guess.

The real value is what we compare with.

3 Write it as a percent

5 and 25 can both be divided by 5.

That keeps the numbers small: 1/5.

Percent means out of 100.

5 times 20 is 100.

So we multiply the top and the bottom by 20.

1 times 20 is 20.

20 out of 100 is 20%.

So the percent error is 20%.

The guess was 20% too high.

4 Check

Let's check: 20% of the actual value should give the error.

20% is 0.2.

0.2 times 25 is 5.

That is the error, 5.

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.