Q: The standard deviation σ for sampling in the case of concrete for construction engineering and management is where X1, X2, X3, X4, ... , Xn = Compressive strengths of the individual cubes N = Number of cubes tested X̄ = Average of series of compressive strength values
(a)√ Σ(X + X̄)² / (N + 1)
(b)√ Σ(X − X̄)² / (N + 1)
(c)√ Σ(X + X̄)² / (N − 1)
(d)√ Σ(X − X̄)² / (N − 1)
Correct Answer: (d)
The correct answer is (a) '√ Σ(X + X̄)² / (N + 1)'. This question from the Quantitative Aptitude & Data Interpretation domain tests knowledge of Numerical Ability.