CTET 2 Math and Science Sep 2015 Paper

Let the box number of cubes = x
Given that
Length of rectangular box = 15 cm
Breadth of rectangular box$=\frac{25}{2}\mathit{c}\mathit{m}$
Height of the rectangular box$=\frac{15}{2}\mathit{c}\mathit{m}$
Volume of rectangular box$=15\times \frac{25}{2}\times \frac{15}{2}{\mathit{c}\mathit{m}}^3$
Volume of the cube$={\mathit{a}}^3$
$={\left(\frac{5}{2}\right)}^3=\frac{125}{8}$
According to question
$\frac{125}{8}\times \mathit{x}=15\times \frac{25}{2}\times \frac{15}{2}$
$\Rightarrow \mathit{x}=\frac{15\times 25\times 15\times 8}{4\times 125}=90$