Problem Solving

BlueDragon2010 wrote:In the formula V = 1/(2r)³, if r is halved then V is multiplied by

A) 64
B) 8
C) 1
D) 1/8
E) 1/64

A quick approach here is to plug in a "nice" number.
Let's plug in r = 1. We get V = 1/[(2)(1)]³ = 1/8

Now let's see what happens when we HALVE r. In other words, we'll plug in r = 1/2.
We get V = 1/[(2)(1/2)]³ = 1

So, when r = 1, V = 1/8, and when r = 1/2, V = 1.

So, when we halve r, V is multiplied by 8

Answer = B

Cheers,
Brent

Hi BlueDragon2010,

This question is perfect for TESTing Values, as Brent's solution showcases.

If you'd rather do algebra, here's how you could solve this problem:

V = 1/(2r)^3

V = 1/8r^3

This is the "starting value"

The question asks us to HALVE the value of r, so we'd then start with this....

V = 1/(r)^3

V = 1/r^3

Compare the denominators of both fractions and you'll see that the denominator went from 8r^3 to r^3, meaning that the denominator was divided by 8. When you divide the denominator of a fraction by 8, the OVERALL fraction becomes 8 times BIGGER.

Final Answer: B

GMAT assassins aren't born, they're made,
Rich