If radius and height of a cylinder increase by 20% and15% respectively. then what is the % change in curved surface area?

% Change in Curved Surface Area is given by 

$\%\mathrm{Change} \mathrm{in} \mathrm{radius} + \%\mathrm{Change} \mathrm{in} \mathrm{height} +\frac{ \%\mathrm{Change} \mathrm{in} \mathrm{radius} \times \%\mathrm{Change} \mathrm{in} \mathrm{height} }{100}$  

$\Rightarrow +20 + 15 + \frac{20\times 15}{100} = 38\%$