Question

An hourglass, composed of two identical cones, is 12 cm tall. The radius of each cone is 3 cm. If you want to fill the bottom half of the hourglass full of salt, how much salt will you need? Explain the method you would use to find the amount of salt.

Answer 1

The volume of a cone is V= (1/3)pi r²h
it was given 
h=12cm
radius=3cm 
the volume of the first cone is V1= 1/3)pi r²h1
where h1= h/2=6cm 
so its volume is V1=1/3)xpix3²x6=56.52cm^3

and since the two cones are identical so V1=V2=56.52cm^3,
we need 56.52cm^3 or salt