0 vote
The sum of the strength and the square of deviation of the 20 cubes is found to be 800 MPa and 304 MPa. The coefficient of variation of the test will be
The sum of the strength and the square of deviation of the 20 cubes is found to be 800 MPa and 304 MPa. The coefficient of variation of the test will be
1). 10%
2). 12%
3). 15%
4). 18%
1 answers
3 vote
Average strength of the cubes, x? = $(\frac{{{\rm{\Sigma x}}}}{{\rm{n}}})$
$(\frac{{{\rm{\Sigma x\bar x}} = \frac{{800}}{{20}} = 40\;MPa}}{{\rm{n}}})$
Standard deviation, σ = $(\sqrt {\frac{{{\rm{\Sigma }}{{\left( {x - \bar x} \right)}^2}}}{{n - 1}}})$
$(\sigma = \sqrt {\frac{{304}}{{20 - 1}}} = \sqrt {\frac{{304}}{{19}}} = 4\;MPa)$
Coefficient of variation, $({C_v} = \frac{\sigma }{{\bar x}} \times 100)$
$({C_v} = \frac{4}{{40}} \times 100 = 10\%)$