Physics quiz question: decimal places resulting from addition/subtraction operation

Physics 205A Quiz 1, fall semester 2015
Cuesta College, San Luis Obispo, CA

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

      93.450 s – 88 s + 0.7 s = ?

(A) 6 s.
(B) 6.2 s.
(C) 6.15 s.
(D) 6.150 s.

Correct answer (highlight to unhide): (A)

For the addition and subtraction operations, the term with the least number of decimal places (shown in gray) determines the number of significant decimal places in the result.

93.450 s – 88 s + 0.7 s.

Since 93.450 s has two decimal places, 88 s has no decimal places, and 0.7 has only one decimal place, then the result of adding or subtracting these numbers will only have no significant decimal places.

Thus:

93.450 s – 88 s + 0.7 s = 6.15 s,

should be truncated with no decimal places to 6 s.

Sections 70854, 70855, 73320
Exam code: quiz01rdBL
(A) : 46 students
(B) : 21 students
(C) : 5 students
(D) : 8 students

Success level: 58%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.71