Find the number of bricks,each measuring $25\, cm \times 12.5\, cm \times 7.5\, cm$,required to construct a wall $12\, m$ long,$5\, m$ high,and $0.25\, m$ thick,if the sand and cement mixture occupies $5\%$ of the total volume of the wall.

$A$ solid metallic sphere of radius $21\, cm$ is melted and recast into a cone with diameter of the base as $21\, cm$. What is the height (in $cm$) of the cone?

$A$ triangle and a parallelogram are constructed on the same base such that their areas are equal. If the altitude of the parallelogram is $100 \, m$,then the altitude of the triangle is

If the ratio of the areas of two squares is $9: 1$,then the ratio of their perimeters is

The dimensions of a field are $20 \text{ m}$ by $9 \text{ m}$. $A$ pit $10 \text{ m}$ long,$4.5 \text{ m}$ wide and $3 \text{ m}$ deep is dug in one corner of the field and the earth removed has been evenly spread over the remaining area of the field. What will be the rise in the height of the field as a result of this operation? (in $m$)

An error of $2 \%$ in excess is made while measuring the side of a square. The percentage of error in the calculated area of the square is.....$\%$