A section drawing shows a foundation wall with a scale of 3/4" = 1'-0". If the wall measures 4.5 inches tall on the drawing, what is the actual height of the foundation wall?
Correct Answer
B) 6 feet
At a scale of 3/4" = 1'-0", each 3/4 inch on the drawing equals 1 foot in reality. Therefore, 4.5 inches on the drawing equals 6 feet actual height (4.5 ÷ 0.75 = 6).
Why This Is the Correct Answer
The scale 3/4" = 1'-0" means that every 3/4 inch on the drawing represents 1 foot in actual construction. To find the actual height, we divide the drawing measurement by the scale factor: 4.5 inches ÷ 0.75 inches = 6. Since each unit represents 1 foot, the actual height is 6 feet.
Why the Other Options Are Wrong
Option A: 4 feet 6 inches
This answer incorrectly assumes a 1:1 ratio between drawing inches and actual feet, treating 4.5 inches on the drawing as 4 feet 6 inches in reality, which ignores the scale conversion.
Option C: 3 feet 4 inches
This answer results from incorrectly multiplying the drawing measurement by the scale factor (4.5 × 0.75 = 3.375 feet ≈ 3'4"), when you should divide to convert from drawing to actual size.
Option D: 5 feet 4 inches
This answer appears to use an incorrect scale conversion, possibly confusing the relationship between the fractional scale and the actual measurement conversion.
Memory Technique
Remember 'Divide to Derive' - you always divide the drawing measurement by the scale factor to get the actual size. For 3/4 scale, think '3/4 = 0.75' and divide by 0.75 to scale up to reality.
Reference Hint
Look up architectural drawing scales and plan reading in the construction documents section, typically found in chapters covering blueprint reading and construction drawings.
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