Posted by **StephanieNZ** on Sunday, March 21, 2010 at 12:58am.

The volume of a sphere is given by:

V=4/3 pie r cubed.

Use the formula, and show your workings, to find out what happens to the volume of a sphere if r is halved and r is trippled?

Please help as this has just completly lost me, i end up with

V = 4/3 Pie r cubed / eight .....for half of r.

- Algebra -
**Reiny**, Sunday, March 21, 2010 at 8:19am
You were correct,

when you cut the radius in half, the volume will be 1/8 of the original.

When you triple the radius, the new volume will be 27 times that of the original.

Look at what happens when we substitute the new radius for r

sub in 3r for the radius

V = (4/3)π(3r)^3

= (4/3)π)(27)r^3

= 27 * (4/3)πr^3

Notice that the volume changes by the cube of the scaling factor,

taking 1/2 ----> (1/2)^3 = 1/8

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