The diameter of a sphere is decreased by $25\%$. By what per cent does its curved surface area decrease (in $\%$)?

$A$ soft drink is available in two packs: $(i)$ a tin can with a rectangular base of length $5 \, cm$ and width $4 \, cm$ having a height of $15 \, cm$,and $(ii)$ a plastic cylinder with a circular base of diameter $7 \, cm$ and height $10 \, cm$. Which container has greater capacity and by how much (in $, cm^3$)?

In a hot water heating system,there is a cylindrical pipe of length $28 \, m$ and diameter $5 \, cm$. Find the total radiating surface in the system. $\left[ \text{Assume } \pi = \frac{22}{7} \right]$ (in $, m^2$)

$A$ metal pipe is $77 \,cm$ long. The inner diameter of a cross section is $4 \,cm$ and the outer diameter is $4.4 \,cm$. Find its outer curved surface area. (in $,cm^{2}$)

Savitri had to make a model of a cylindrical kaleidoscope for her science project. She wanted to use chart paper to make the curved surface of the kaleidoscope (see figure). What would be the area of chart paper required by her,if she wanted to make a kaleidoscope of length $25\, cm$ with a $3.5\, cm$ radius (in $, cm^{2}$)? You may take $\pi=\frac{22}{7}$.

Find the surface area of a sphere of diameter $21 \, cm$. Assume $\pi = \frac{22}{7}$. (in $, cm^{2}$)