To calculate the percent error, we use the following formula:

$\text{Percent Error} = \left( \frac{|\text{Estimated Value} - \text{Actual Value}|}{\text{Actual Value}} \right) \times 100$

From the question:

• Estimated Value = 51
• Actual Value = 60

Now, applying the formula:

$\text{Percent Error} = \left( \frac{|51 - 60|}{60} \right) \times 100 = \left( \frac{9}{60} \right) \times 100 = 15\%$

So, the correct answer is 15%.

Would you like more details on this calculation or have any questions?

Here are five related questions you might explore:

1. What does percent error represent in practical applications?
2. How does percent error differ from percent difference?
3. How can rounding affect percent error in measurements?
4. Can percent error be negative, and if so, what does it mean?
5. How can you minimize percent error in scientific experiments?

Tip: Always use absolute values when calculating percent error to ensure the result is positive.