A spherical balloon is inflated until its radius is 20% greater than before. By what percentage does its outer surface increase?

A sphere's surface is 4π$r^2$, so it scales as the SQUARE of the radius: the new surface is $1.2^2=1.44$ times the old, an increase of 44%. The trap 20% applies the linear growth straight to the surface; 40% doubles the 20% and drops the small 0.04 term that squaring produces; 72.8% is the increase in the balloon's VOLUME, since $1.2^3=1.728$, a cubic answer offered where a surface was asked.