200 wooden balls each of diameter 70 mm are to be painted. Then the cost of painting these balls at ${\text{10 paise/cm}}^{\text{2}}$  is

$r=35\text{ mm=}\frac{35}{10}\text{cm}$ 

S.A of 200 sphere $200.4\pi r^2$

$=\mathrm{200.4.}\frac{22}{7}.\frac{35}{10}.\frac{35}{10}$

$=30800{\text{ cm}}^2$

Cost per  ${\text{1cm}}^{\text{2}}=10\text{paise}$

$\therefore$  total cost $=\text{Rs}\text{. 30800}\times \frac{10}{100}$

$=\text{Rs}.3080$