A detail drawing is scaled at 1/2" = 1'-0". If a dimension on the drawing measures 3 inches, what is the actual dimension?
Correct Answer
D) 6 feet
At 1/2" = 1'-0" scale, each 1/2 inch on the drawing represents 1 foot actual. Therefore, 3 inches on the drawing equals 3 ÷ 0.5 = 6 feet actual dimension.
Why This Is the Correct Answer
At 1/2" = 1'-0" scale, every half inch on the drawing represents one foot in reality. To find the actual dimension, divide the drawing measurement by the scale factor: 3 inches ÷ 0.5 inches = 6. Since each unit represents 1 foot, the actual dimension is 6 feet. This scale conversion is fundamental in construction plan reading.
Why the Other Options Are Wrong
Option A: 6 inches
This answer incorrectly assumes a 1:1 scale ratio, simply doubling the drawing measurement. It fails to account for the fact that the scale represents feet, not inches, in the actual dimension.
Option B: 3 feet
This answer treats the 3-inch measurement as if it directly equals 3 feet without applying the scale conversion. It ignores the 1/2" = 1'-0" scale relationship entirely.
Option C: 18 inches
This answer incorrectly multiplies 3 inches by 6, possibly confusing the scale conversion process. It fails to properly convert from the drawing scale to actual feet dimensions.
Memory Technique
Remember 'Half-inch Helper': When you see 1/2" = 1'-0", think 'divide drawing inches by 0.5 to get actual feet.' The scale fraction's denominator (0.5) is your division key.
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