Explanation:

- The original volume of the cylinder is calculated as $V=\pi r^{2}h$.

- The radius is increased by 20%, making it $1.2r$.

- The height is decreased by 45%, making it $0.55h$.

- New volume becomes $V^{\prime }=\pi (1.2r{)}^2(0.55h)=\pi \times 1.44r^2\times 0.55h$.

- The ratio of new volume to original volume is $1.44\times 0.55=0.792$.

- Thus, the new volume is 79.2% of the original, indicating a 20.8% decrease.

- Option 2: Decrease 20.8% is the correct answer.

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