A detail drawing shows a scale of 3/4" = 1'-0". If a dimension measures 2.25 inches on the drawing, what is the actual dimension?
Correct Answer
B) 3 feet 0 inches
At 3/4" = 1'-0" scale, 2.25 inches on the drawing equals 2.25 ÷ 0.75 = 3 feet actual dimension.
Why This Is the Correct Answer
To convert from drawing dimension to actual dimension with a scale of 3/4" = 1'-0", you divide the drawing measurement by the scale factor. The scale factor is 3/4 = 0.75 inches per foot. Dividing 2.25 inches by 0.75 gives us 3, which represents 3 feet. This is the correct mathematical relationship for architectural scale conversions.
Why the Other Options Are Wrong
Option A: 2 feet 6 inches
This answer results from incorrectly multiplying 2.25 by 0.75 instead of dividing, which gives 1.6875 feet or approximately 2 feet 6 inches - the wrong operation was performed.
Option C: 3 feet 6 inches
This answer suggests 3.5 feet, which would result from using an incorrect scale factor or mathematical error in the conversion process.
Option D: 4 feet 0 inches
This answer of 4 feet would result from incorrectly assuming a 1:1 scale or using a wrong conversion factor in the calculation.
Memory Technique
Remember 'D-D-A': Drawing Divided by Decimal scale = Actual size. Also remember 3/4 scale is common and equals 0.75 - practice this conversion until automatic.
Reference Hint
Look up architectural drawing scales and scale conversions in the construction documents section of your reference materials, typically found in drafting or blueprint reading chapters.
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