Hi there,
volume of cylinder=πr^2h
if new radius=2r
and new height is h/2
new volume=2π4r^2*h/2.
therefore the volume will be doubled
i hope this helps u.. nd pls smash the thanks button 
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given :
radius is doubled in a cylinder
height is halved

need to find out :
the percent change in volume  

solution :
we know that volume of cylinder =  \pi r² h
the radius according to the question =  2r
the height according to the question = h/2
∴ the new volume = 2 \pi  4r² h/2

by this we can understand that the volume would double
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