Answer: Ratio of new volume to original volume is 2:1.
Explanation:
Let the radius of cylinder be 'r'
Let the height of cylinder be 'h'
Original volume of cylinder will be

If radius get doubled,
New radius be '2r'
If height get halved,
New height be will be

so, Volume of cylinder becomes

Ratio of new volume to the original volume is given by

Hence, Ratio of new volume to original volume is 2:1.