A section drawing shows a foundation wall with a scale of 1/4" = 1'-0". If the wall thickness measures 2 inches on the drawing, what is the actual wall thickness?
Correct Answer
B) 8 inches
With a scale of 1/4" = 1'-0", each 1/4 inch represents 1 foot (12 inches) actual. Therefore, 2 inches on the drawing represents 8 feet, but since this is a wall thickness, 2 ÷ 0.25 = 8 inches actual thickness.
Why This Is the Correct Answer
With a scale of 1/4" = 1'-0", every 1/4 inch on the drawing represents 12 inches in reality. To find the actual dimension, we divide the drawing measurement by the scale factor: 2 inches ÷ 0.25 = 8. Since we're dealing with a wall thickness (a relatively small dimension), the result is 8 inches, not 8 feet. This makes sense as typical foundation walls range from 6-12 inches thick.
Why the Other Options Are Wrong
Option A: 6 inches
6 inches would result from incorrectly calculating 2 × 3 instead of using the proper scale conversion formula.
Option C: 12 inches
12 inches would result from mistakenly thinking each inch on the drawing equals 6 inches actual, which is not the given scale.
Option D: 16 inches
16 inches would result from incorrectly multiplying 2 × 8 instead of dividing by the scale factor.
Memory Technique
Remember 'Quarter Scale, Divide by Quarter': When you see 1/4" scale, divide the drawing measurement by 0.25 to get actual inches
Reference Hint
Florida Building Code, Chapter 18 - Soils and Foundations, or architectural drafting standards section
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