To find the percentage error in this situation, we can use the formula for percentage error:
\[ \text{Percentage Error} = \left( \frac{\text{Actual Value} - \text{Expected Value}}{\text{Expected Value}} \right) \times 100 \]
In this case:
- Actual Value (the change given by the trader) is 500.
- Expected Value (the correct change that should be given) is 400.
Now, substituting these values into the formula:
\[ \text{Percentage Error} = \left( \frac{500 - 400}{400} \right) \times 100 \]
Calculating the error:
\[ \text{Percentage Error} = \left( \frac{100}{400} \right) \times 100 = 0.25 \times 100 = 25% \]
Thus, the percentage error is 25%.