# Thread: Find surface area to volume ratio

1. ## Find surface area to volume ratio

1st find SA, then volume, then the ratio

1. 2cm x 3cm x 4cm
2. 6 cm x 8 cmx 10cm

2. Are those cuboids?

If so,

$Volume_{cuboid} = l\times b \times h$

$Volume_{sphere} = \dfrac43 \pi r^3$

$SA_{cuboid} = 2 lb + 2 lh + 2 lh$

$SA_{sphere} = 4\pi r^2$

Ratio will be simple then.

3. I know the formulas, it just doesn't work when I do it or is a decimal.

4. Why not?

a) $Volume = lbh = (2)(3)(4) = 24 cm^3$

$SA = 2(2)(3) + 2(3)(4) + 2(2)(4) = 12 + 24 + 16 = 52 cm^2$

Ratio = 24 : 52 = 6 : 13

5. Thanks, I already got that one. It's just the last two with decimals that I can't solve.

6. $Volume = \dfrac43 \pi (4)^3 = \dfrac43 \pi (64) = \dfrac{256\pi}{3} cm^3$

$SA = 4 \pi (4)^2 = 64 \pi\ cm^2$

Ratio = 256/3 : 64 = 4 : 3

7. Thank you, thank you, thank you!
But I'm still getting a decimal on the last one D:

8. Really? =/

$Volume = \dfrac43 \pi (0.75)^3 = \dfrac{9\pi}{16}$ cm^3

$SA = 4\pi (0.75)^2 = \dfrac{9\pi}{4}$ cm^2

Ratio = 9/16 : 9/4 = 4 : 16 = 1 : 4

9. Yeah, I know, but I missed class on Thursday/Friday so I wasn't exactly taught how to do it.
Also, for #2, the ratio 188:225 isn't right, is it?

10. Oo

$Volume = (8)(6)(10) = 480$ cm^3

$SA = 2(8)(6) + 2(8)(10) + 2(6)(10) = 376$ cm^2

Ratio = 480: 376 = 60 : 47