ACT (Enhanced)ScienceEasy
A student measures the mass of a rock sample three times: 15.2 g, 15.3 g, and 15.2 g. The known actual mass of the rock is 16.5 g. Which of the following statements best describes the student's measurements?
- AThe measurements are neither precise nor accurate.
- BThe measurements are both precise and accurate.
- CThe measurements are accurate but not precise.
- DThe measurements are precise but not accurate.
Show answer & explanationAnswer & explanation
Correct answer: D. The measurements are precise but not accurate.
The measurements are close to each other (15.2, 15.3, 15.2), indicating good precision. However, they are consistently far from the true value of 16.5 g, meaning they are not accurate.
Why the other options are wrong
- A. The measurements are clustered, indicating precision, even if they are not accurate.
- B. For measurements to be accurate, they must be close to the true value, which these are not.
- C. For measurements to be accurate, they must be close to the true value. For them to be imprecise, they would be spread out.
Precision vs. Accuracy
Precision refers to the closeness of two or more measurements to each other, while accuracy refers to the closeness of a measurement to the true or accepted value.
- High precision means reproducible results.
- High accuracy means results are close to the true value.
- Measurements can be precise but not accurate, or vice versa, or both/neither.
Memory trick: Aim true for accuracy, hit same for precision.