A detail drawing shows a wall section at 3/4" = 1'-0" scale. If the wall thickness measures 1.5 inches on the drawing, what is the actual wall thickness?
Correct Answer
C) 24 inches
At 3/4" = 1'-0" scale, each 3/4 inch on the drawing equals 12 inches actual. Since 1.5 ÷ 0.75 = 2, and 2 × 12 = 24 inches actual thickness.
Why This Is the Correct Answer
Option C is correct because at 3/4" = 1'-0" scale, we need to determine how many scale units fit into the measured drawing dimension, then multiply by the actual size each unit represents. The 1.5 inches on the drawing divided by 0.75 inches (the scale unit) equals 2 scale units. Since each scale unit represents 12 inches actual, 2 × 12 = 24 inches actual wall thickness.
Why the Other Options Are Wrong
Option B: 12 inches
Option B is wrong because 18 inches would result from an incorrect calculation, possibly from multiplying 1.5 × 12 directly without properly accounting for the 3/4 inch scale ratio.
Option D: 2 feet
Option A is wrong because 2 feet (24 inches) is the correct answer in inches, but this option expresses it in feet, making it appear smaller than the actual calculated value.
Memory Technique
Remember 'DMA': Divide drawing measurement by scale unit, Multiply by Actual size per unit. For 3/4" scale, think '3/4 gets you 12' - so divide by 0.75, then multiply by 12.
Reference Hint
Look up architectural drawing scales and scale conversion methods in the construction documents and blueprint reading sections of your reference materials.
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