- anonymous

The two square pyramids are similar. Find the total volume of both pyramids if the ratio of their surface areas is 9/16.
A. 545 inches cubed
B. 546 inches cubed
C. 554 inches cubed
D. 564 inches cubed

- katieb

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- anonymous

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- anonymous

- anonymous

please help

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## More answers

- Hero

@pooja195, are you going to help?

- anonymous

I really need desperate help. I'm horrible at ratios and anything having to do with similar figures.

- Hero

It's getting a bit late for me.

- pooja195

V1 / V2 = (L1 / L2)^3

- anonymous

uhhhhhhh

- anonymous

drawing a blank :(

- pooja195

lol
v=volume
l=length of a dimension

- anonymous

i know that i just dont know how to put the numbers and that formula together

- pooja195

gimmie a sec...

- anonymous

ok

- pooja195

Let's use volume formula of pyramid
V = 1/3 * base area * height

- pooja195

V = 1/3 * base area * height
V1 = 1/3 * (x)^2 * 6
V2 = 1/3 * (12)^2 * y

- anonymous

so what would be y?

- pooja195

look
http://prntscr.com/837zqu

- pooja195

x is the side length of the base of the small pyramid
y is the height of the larger pyramid

- anonymous

okay so how do i figure out the y then, im sorry i sound dumb im just confused. i know the formula but how do i do it wen i dont know the y

- pooja195

lol you're not dumb! :)
Here see if you understand this :)
Let's use volume formula of pyramid
Volume = 1/3 * base area * height
Given:
V1 = 1/3 * (x)^2 * 6
V2 = 1/3 * (12)^2 * y
We can find the scale factor
A1 / A2 = (L1 / L2 ) ^2 = 9/16
L1 / L2 = √ 9/16 = 3/4

- anonymous

ok so the scale factor is 3/4. what's next

- pooja195

lol you're not dumb! :)
Here see if you understand this :)
Let's use volume formula of pyramid
Volume = 1/3 * base area * height
Given:
V1 = 1/3 * (x)^2 * 6
V2 = 1/3 * (12)^2 * y
We can find the scale factor
A1 / A2 = (L1 / L2 ) ^2 = 9/16
L1 / L2 = √ 9/16 = 3/4
L1 = 3/4 * L2
Let L2 = y , then L1= 3/4* L2
x= 3/4*y
V1 = 1/3 * (3/4 *y ) * 6
V2 = 1/3 * (12)^2 * y

- pooja195

The scale factor is 3/4 to go from the bigger pyramid to the smaller pyramid

- pooja195

understood so far?

- anonymous

No... i'm sorry. everything is confusing me..

- pooja195

We can find the scale factor
A1 / A2 = (L1 / L2 ) ^2 = 9/16
L1 / L2 = √ 9/16 = 3/4
The scale factor is 3/4 to go from the bigger pyramid length dimension to the smaller pyramid length dimension.
The scale factor is 4/3 to go from the smaller pyramid length dimension to the bigger pyramid length dimension.
V1 = 1/3 * (3/4 * 12) ^2 * 6
V2 = 1/3 * (12)^2 * (6 * 4/3)

- pooja195

Is that better?

- anonymous

I got 384

- anonymous

for V2

- pooja195

good how bout V1?

- anonymous

24

- pooja195

Not quite...
V1 = 1/3 * (3/4 * 12) ^2 * 6= 162

- anonymous

okay so what do i do after that

- anonymous

if you don't mind kind of fast forwarding a little bit im on a timed assignment. i dont mean to sound rushy :(

- pooja195

dont worry :-) we're almost done! :D
384+162=?

- anonymous

546

- pooja195

good job and that would be our final answer :)

- anonymous

thank you so much

- pooja195

;) no probs ^-^

- pooja195

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