Moisture (water) content calculation from weighing data A soil sample is tested for water content with: container weight = 260 g; container + wet soil = 320 g; container + dry soil = 310 g. Compute the moisture content (percent, by mass of dry soil).

Introduction / Context:
Water content (moisture content) is defined as the mass of water divided by the mass of dry soil, expressed as a percentage. It is a core parameter for compaction, consistency limits, and phase-relationship calculations in geotechnical engineering.

Given Data / Assumptions:

• W_c (container) = 260 g.
• W_c+w (container + wet soil) = 320 g.
• W_c+d (container + dry soil) = 310 g.
• No mass loss from soil solids during drying.

Concept / Approach:

Compute masses of wet and dry soil by subtracting container mass, then obtain water mass as the difference. Water content w(%) = (mass of water / mass of dry soil) * 100.

Step-by-Step Solution:

Verification / Alternative check:

Cross-check: Container cancels; water mass equals difference between wet and dry combined weights (320 − 310 = 10 g), consistent with the calculation.

Why Other Options Are Wrong:

15%, 18%, 25%, and 12.5% arise from using wet mass in the denominator or arithmetic slips.

Common Pitfalls:

Dividing by wet soil mass instead of dry; forgetting to subtract the container mass correctly.

Final Answer:

20%