Question

the density of copper is listed as 8.94 g/cm3. two students each make three density determinations of samples of the substance. student a’s results are 7.3 g/ml, 9.4 g/ml, and 8.3 g/ml. student b’s results are 8.4 g/cm3 , 8.8 g/cm3, and 8.0 g/cm3. compare the two sets of results in terms of precision and accuracy.
○ student a is more precise but less accurate than student b
○ student a is more accurate and precise than student b
○ student a is more accurate but less precise than student b
○ student b is more accurate and precise than student a

Explanation:

1. Accuracy: How close results are to the true value (8.94 g/cm³).

• Student A's results: 7.3, 9.4, 8.3 g/mL (note: 1 mL = 1 cm³, so units match). The average is $\frac{7.3 + 9.4 + 8.3}{3} = \frac{25}{3} \approx 8.33$ g/cm³.
• Student B's results: 8.4, 8.8, 8.0 g/cm³. The average is $\frac{8.4 + 8.8 + 8.0}{3} = \frac{25.2}{3} = 8.4$ g/cm³.

Student B’s average (8.4) is closer to 8.94 than Student A’s (8.33), so B is more accurate.

1. Precision: How close results are to each other (smaller range/standard deviation).

• Student A’s range: $9.4 - 7.3 = 2.1$ g/cm³.
• Student B’s range: $8.8 - 8.0 = 0.8$ g/cm³.

Student B’s results are closer together (smaller range), so B is more precise.

Answer:

D. Student B is more accurate and precise than student A