A detail drawing shows a scale of 3" = 1'-0". If a dimension measures 1.5 inches on the drawing, what is the actual dimension?
Correct Answer
B) 6 inches
At 3" = 1'-0" scale, each inch on the drawing represents 4 inches actual (12" ÷ 3" = 4). Therefore, 1.5 inches on the drawing equals 1.5 x 4 = 6 inches actual dimension.
Why This Is the Correct Answer
The scale 3" = 1'-0" means that 3 inches on the drawing represents 12 inches (1 foot) in reality. This creates a ratio where each inch on the drawing equals 4 inches actual (12÷3=4). When you multiply the drawing measurement of 1.5 inches by this ratio factor of 4, you get 6 inches actual dimension.
Why the Other Options Are Wrong
Option A: 4 inches
This answer of 4 inches would be correct if the drawing measurement was exactly 1 inch, but since we have 1.5 inches on the drawing, the actual dimension must be larger than 4 inches.
Option C: 8 inches
This answer incorrectly applies a ratio factor of approximately 5.33, which doesn't correspond to the given scale of 3" = 1'-0".
Option D: 18 inches
This answer of 18 inches incorrectly multiplies 1.5 by 12 instead of by 4, suggesting a misunderstanding of how the scale ratio works.
Memory Technique
Remember 'Scale Factor = Reality ÷ Drawing' - for 3"=1'-0", that's 12÷3=4, so every drawing inch equals 4 real inches.
Reference Hint
Look up architectural drawing scales and scale conversion in the construction documents or blueprint reading sections of your reference materials.
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