A patio subgrade must drain at 2 percent away from the building for 20 feet. What total drop is required?
Correct Answer
C) 4.8 inches.
Two percent means 0.02 foot of drop per foot of run. Over 20 feet, that is 0.4 foot, or 4.8 inches.
Why This Is the Correct Answer
Two percent means 0.02 foot of drop per foot of run. Over 20 feet, that is 0.4 foot, or 4.8 inches.
Why the Other Options Are Wrong
Option A: 0.24 inch.
0.24 inch. is below the supported result for earthwork grading calculation; it likely omits allowance, conversion, coverage, or final round-up.
Option B: 2.4 inches.
2.4 inches. is below the supported result for earthwork grading calculation; it likely omits allowance, conversion, coverage, or final round-up.
Option D: 24 inches.
24 inches. is above the supported result for earthwork grading calculation; it likely double-counts allowance, uses the wrong unit, or rounds too early.
Memory Technique
Earthwork Grading cart for Checking Finish-Grade: percent first, means second, whole the controlling choice last.
Reference Hint
Study anchor (closed-book): memorize Earthwork grading calculation from 2025 California Building Code, California Code of Regulations Title 24 / Title 24 California Building Code site drainage and grading; know the rule or calculation trigger without relying on exam-room lookup.
More Class B Trade Questions
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