Physics quiz question: significant figures addition rule

Physics 205A Quiz 1, fall semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 1.12

[Version 1]

Evaluate the following calculation, using an appropriate number of significant figures and/or decimal places.

      4.26 g + 10.0 mg = ?

(A) 4.27 g.
(B) 4.3 g.
(C) 4.36 g.
(D) 4.4 g.

Correct answer: (A)

In order to apply the addition-subtraction rule of limiting decimal places, the 10.0 mg is converted into grams such that:

4.26 g + 10.0 mg = 4.26 g + 0.0100 g = 4.27 g,

limited to two decimal places by the first term.

Student responses
Sections 70854, 70855
(A) : 15 students
(B) : 8 students
(C) : 3 students
(D) : 2 students

[Version 2]

[3.0 points.] Evaluate the following calculation, using an appropriate number of significant figures and/or decimal places.

      4.26 g + 100.0 mg = ?

(A) 4.27 g.
(B) 4.3 g.
(C) 4.36 g.
(D) 4.4 g.

Correct answer: (C)

In order to apply the addition-subtraction rule of limiting decimal places, the 10.0 mg is converted into grams such that:

4.26 g + 100.0 mg = 4.26 g + 0.1000 g = 4.36 g,

again, limited to two decimal places by the first term.

Student responses
Sections 70854, 70855
(A) : 1 student
(B) : 3 students
(C) : 16 students
(D) : 5 students

"Difficulty level": 57%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.2