The diameters of two concentric circles are $8\, cm$ and $10\, cm$. The area of the region between them is

One of the diagonals of a rhombus is double the other diagonal. Its area is $25\, cm^{2}$. The sum of the diagonals is.......$cm$

How many tiles,each $4 \, dm$ square,will be required to cover the floor of a room $8 \, m$ long and $6 \, m$ broad?

$A$ rectangular farm has to be fenced on one long side, one short side, and the diagonal. If the cost of fencing is ₹ $10$ per $m$, the area of the farm is $1200 \ m^2$, and the short side is $30 \ m$ long, how much would the job cost? (in ₹)

$A$ rectangular field costs $Rs. 110$ for levelling at $50$ $paise$ per square metre. If the ratio of length to breadth is $11: 5$, find the length of the field (in $m$).

Each side of an equilateral triangle is increased by $1.5 \%$. The percentage increase in its area is......$\%$