Civil Engineering - UPSC Civil Service Exam Questions - Discussion

18. 

A plot of land 60°m x 20 m is measure steel tape. If the standard error of length width measurements is taken as ± 1 cm, the standard error of the area of the plot be

[A]. ± 0.1414 m2
[B]. ± 0.566 m2
[C]. ± 0.632 m2
[D]. ± 0.8484 m2

Answer: Option C

Explanation:

No answer description available for this question.

Pranay said: (Sep 12, 2015)  
How? Please explain.

Raj said: (Sep 20, 2015)  
standard error of A = ^,A = SQRT[(^,A/^,X)^2 ^,X^2+(^,A/^,Y)^2 ^,Y^2].

Abhay said: (Feb 2, 2016)  
Std Error of A = σA = Sqrt{(δA/δX)2σX2+ (δA/δY)2σY2}

A = X * Y.

X = 60 +/- 0.01m , Y = 20m +/- 0.01m.

Since [(δA/δX) = Y and (δA/δY) = X.

Substituting value of X and Y with either +ve error or -ve error.

σA = Sqrt{Y2*(0.01)2 + X2*(0.01)2}

= +/- 0.6325.

Rakesh said: (Dec 19, 2016)  
Please give correct explanation to understand the solution.

Arpon said: (Oct 11, 2017)  
How ? can't understand. Please explain.

Arpon said: (Oct 11, 2017)  
Here, error = √[ {(length)^2 * (error in length)^2} + {(width)^2 * (error in width)^2}].

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