BECE Mathematics 2018 Paper

Concept:A cylinder's volume is the product of its circular base area $\pi r^2$ and its height $h$.The formula is $V = \pi r^2 h$. Here we know the volume and height, so we solve for the base radius $r$.Explanation:Write the volume formula for a cylinder:$$V = \pi r^2 h$$Substitute the given values $V = 20\pi\ \text{cm}^3$ and $h = 5\ \text{cm}$:$$20\pi = \pi \times r^2 \times 5$$Divide both sides by $\pi$ to remove it from the equation:$$20 = 5r^2$$Divide both sides by 5:$$r^2 = 4$$Take the positive square root, because the radius cannot be negative:$$r = \sqrt{4} = 2$$So the base radius is $2\ \text{cm}$.Answer:The base radius is $2\ \text{cm}$, which is Option B.