Jharne De and Ranjana Kumar Solutions for Chapter: Perimeter and Area, Exercise 1: Mental Maths

The distance around a circular region is called its _____.

If the area of a square is $64 {\mathrm{cm}}^2$, then its perimeter is _____.

If the length of the side of a regular octagon is $4 \mathrm{cm}$, then its perimeter is _____ $\mathrm{cm}$.

If the side of a square is doubled, then its perimeter becomes _____ times the original perimeter.

If both the height and base of a triangle are halved, then its area becomes _____ times the original area. (half/one-fourth/one-third)

If the circumference of a circle is $154$ $\mathrm{cm}$, then its radius is _____ $\mathrm{cm}$.

If the area of a circle is $314 {\mathrm{m}}^2$, then its diameter is_____ $\mathrm{m}$. (Use $\pi =3.14$)

If the area of a circular ring with outer and inner radii as $R$ and $r$, respectively is $\pi ($ $R^2$_____$r^2)$