According to the probability density function given, it is found that 0.2813 = 28.13% of steel plates have elongations greater than 25%.
Researching the problem on the internet, it is found that the elongation of steel plates treated with aluminum are random with probability density function given as follows:
[tex]p(x) = \frac{x}{400}, 15 \leq x \leq 30[/tex]
The proportion of steel plates have elongations greater than 25% is given by:
[tex]p = \int_{25}^{30} p(x) dx[/tex]
[tex]p = \int_{25}^{30} \frac{x}{400} dx[/tex]
[tex]p = \frac{x^2}{800}|_{x = 25}^{x = 30}[/tex]
Applying the Fundamental Theorem of Calculus:
[tex]p = \frac{30^2}{800} - \frac{25^2}{800}[/tex]
[tex]p = 0.2813[/tex]
0.2813 = 28.13% of steel plates have elongations greater than 25%.
You can learn more about probability density functions at https://brainly.com/question/14683948