If the radius of a right circular cylinder open at both the ends is decreased by $25\%$ and the height of the cylinder is increased by $25\%$, then the surface area of the cylinder thus formed is:

For an open cylinder, the surface area is given by $2\pi rh$. If the radius is decreased by 25%, the new radius is $0.75r$. If the height is increased by 25%, the new height is $1.25h$. The new surface area becomes $2\pi(0.75r)(1.25h) = 0.9375(2\pi rh)$. This represents a decrease of $(1 - 0.9375) = 0.0625$, which is 6.25%. The surface area decreases by 6.25%.

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