Exercise 12.1

The radii of two circles are $19 \mathrm{c}\mathrm{m}$ and $9 \mathrm{c}\mathrm{m}$ respectively. Find the radius of the circle which has circumference equal to the sum of the circumferences of the two circles. 

The radii of two circles are $8 \mathrm{c}\mathrm{m}$ and $6 \mathrm{c}\mathrm{m}$ respectively. Find the radius of the circle having area equal to the sum of the areas of the two circles. $\left(\mathrm{u}\mathrm{s}\mathrm{e}\pi =\frac{22}{7}\right)$

Given figure depicts an archery target marked with its five-scoring areas from the centre outwards as Gold, Red, Blue, Black and White. The diameter of the region representing Gold score is $21 \mathrm{c}\mathrm{m}$ and each of the other bands is $10.5 \mathrm{c}\mathrm{m}$ wide. Find the area of each of the five scoring regions. $\left(\mathrm{use\pi }=\frac{22}{7}\right)$

The wheels of a car are of diameter $80 \mathrm{c}\mathrm{m}$ each. How many complete revolutions does each wheel make in 10 minutes when the car is traveling at a speed of $66 \mathrm{k}\mathrm{m}$ per hour? $\left(\mathrm{use} \pi =\frac{22}{7}\right)$

If the perimeter and the area of a circle are numerically equal, then the radius of the circle is (Use $\pi =\frac{22}{7}$).