# DuBois Formula Problem

1. Jun 2, 2006

### swears

Ok, my teacher did this problem today, but there is 1 step I don't understand. If someone could explain to me how it's done, that'd be great.

Here's the problem:

Using the DuBois formula: S = 0.01W^(0.25) H^(.75)

Solve for H(Height) as a function of S (Surface Area) for people of fixed weight(W) 70

S = 0.01(70)^(.25) H^(.75)

S = 100/70^(.25) = H^(.75)
//This is the step I don't understand. Where does the 100 come from and what happened to 0.01? Am I an idiot?

34.57 S = H^(.75)

34.57^(4/3) S^(4/3) = H

H = 112.6 S^(4/3)

Last edited: Jun 2, 2006
2. Jun 2, 2006

### arildno

Evidently, you don't understand it, since you are too sloppy about how you write stuff.

3. Jun 2, 2006

### AKG

It should not be "S =" at the beginning, it should be "S x", i.e. "S times". The whole thing should be:

S = 0.01(70)^(.25) H^(.75)

S x 100/70^(.25) = H^(.75)

34.57 S = H^(.75)

34.57^(4/3) S^(4/3) = H

H = 112.6 S^(4/3)

4. Jun 2, 2006

### swears

Thanks for the support

5. Jun 2, 2006

### swears

AGK, how did you swap S and H^(.75)

6. Jun 2, 2006

### Hootenanny

Staff Emeritus
$$S = 0.01(70^{0.25}) \cdot H^{0.75}$$

$$S = \frac{70^{0.25}}{100}\cdot H^{0.75}$$

$$\frac{S}{H^{0.75}} = \frac{70^{0.25}}{100}$$

$$\frac{1}{H^{0.75}} = \frac{70^{0.25}}{100S}$$

$$H^{0.75} = \frac{100S}{70^{0.25}}$$

$$H^{0.75} = S \times \frac{100}{70^{0.25}}$$

Does that make more sense now?

~H

7. Jun 2, 2006

### swears

Yes, that makes more sense, thanks.

I'm not sure how you got the 1 in step 4 though.

8. Jun 2, 2006

### Hootenanny

Staff Emeritus
From here;

$$\frac{{\color{red}S}}{H^{0.75}} = \frac{70^{0.25}}{100}$$

Just divide both sides 'S'

$$\frac{1}{H^{0.75}} = \frac{70^{0.25}}{100{\color{red}S}}$$

Do you see?

~H

9. Jun 2, 2006

Yes, Thanks.