20110902

Physics quiz question: subtracting mass measurements

Physics 205A Quiz 1, fall semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 1.15(a)

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

8.44 g – 7.3 g = ?

(A) 1.0 g.
(B) 1.1 g.
(C) 1.10 g.
(D) 1.14 g.

Correct answer (highlight to unhide): (B)

While 8.44 g has three significant figures (shown in green), and 7.3 g has two significant figures, 8.44 g has two decimal places (shown in gray), while 7.3 g has only one decimal place.

For addition and subtraction operations, the term with the least number of decimal places determines the number of significant decimal places in the result:

8.44 g – 7.3 g = 1.14 g.

Thus the result of this subtraction has only one decimal place, and the resulting calculation should be truncated to 1.1 g.

Sections 70854, 70855
Exam code: quiz01unI7
(A) : 1 student
(B) : 54 students
(C) : 0 students
(D) : 3 students

"Success level": 95%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.27