# Proportions

• Apr 17th 2008, 06:00 PM
PandaPanda
Proportions
Just a couple of simple questions I'm having trouble on.

6. y is directly proportional to the square of x, and y = 48 when x = 4. What is y when x = 24?

10. y is inversely proportional to x, and y = 32 when x = 4. what is y when x = 18?

Thanks.
• Apr 17th 2008, 06:02 PM
colby2152
Quote:

Originally Posted by PandaPanda
Just a couple of simple questions I'm having trouble on.

6. y is directly proportional to the square of x, and y = 48 when x = 4. What is y when x = 24?

10. y is inversely proportional to x, and y = 32 when x = 4. what is y when x = 18?

Thanks.

$\displaystyle y=cx^2$

$\displaystyle 48=16c$

$\displaystyle c=3$

$\displaystyle y(24)=3*24^2$
• Apr 17th 2008, 06:03 PM
Jen
Quote:

Originally Posted by PandaPanda
Just a couple of simple questions I'm having trouble on.

6. y is directly proportional to the square of x, and y = 48 when x = 4. What is y when x = 24?

10. y is inversely proportional to x, and y = 32 when x = 4. what is y when x = 18?

Thanks.

When something is directly proportional it means,
$\displaystyle y=kx$ where k is some constant.

Inversly proportional means,
$\displaystyle y=\frac{k}{x}$

so if y is directly proportional to the square of x then,
$\displaystyle y=kx^2$

Then use your values given to solve for K.

Hope that helps! :)
• Apr 17th 2008, 06:14 PM
PandaPanda
Thanks.

What confused me was there were problems stating "y varies directly/inversely with x" and "y is directly/inversely proportional to x"

What's the difference?
• Apr 17th 2008, 06:50 PM
Jen
Quote:

Originally Posted by PandaPanda
Thanks.

What confused me was there were problems stating "y varies directly/inversely with x" and "y is directly/inversely proportional to x"

What's the difference?

Are you still needing to know the difference, or did I make it clear enough in my last post?