# Thread: Scale model - volume

1. ## Scale model - volume

An artist plans to make a large sculpture of a person out of solid marble. She first makes a small scale model out of clay, using a scale of 1 inch = 2 feet. The scale model weighs 1.3 pounds. Assuming that a cubic foot of clay weighs 150 pounds and a cubic foot of marble weighs 175 pounds, how much will the large marble sculpture weigh? Explain your reasoning.

I am stuck here, can anyone get me started in the right direction?

2. An artist plans to make a large sculpture of a person out of solid marble. She first makes a small scale model out of clay, using a scale of 1 inch = 2 feet. The scale model weighs 1.3 pounds. Assuming that a cubic foot of clay weighs 150 pounds and a cubic foot of marble weighs 175 pounds, how much will the large marble sculpture weigh? Explain your reasoning.
if 1 cubic ft of clay weighs 150 and the model weighs 1.3, then the model is 1.3/150 cubic feet. multiply by 12 to get in cubic inches.sp its 15.6/150 cubic inches.
next, if the scale is 1 in= 2 ft, then 1 cubic inch= 8 cubic ft. so, multiply 15.6/150 by 8= 124.8/150 cubic ft.
now multiply by 175, the weight of a cubic ft of marble. so the answer would be about 145.6 pounds

3. I am not following exactly...

4. Is this correct? I am not following the conversions

5. Hello igottaquestion
Originally Posted by igottaquestion
An artist plans to make a large sculpture of a person out of solid marble. She first makes a small scale model out of clay, using a scale of 1 inch = 2 feet. The scale model weighs 1.3 pounds. Assuming that a cubic foot of clay weighs 150 pounds and a cubic foot of marble weighs 175 pounds, how much will the large marble sculpture weigh? Explain your reasoning.

I am stuck here, can anyone get me started in the right direction?
This question is all about ratios.

When dealing with a scale which has mixed units (in this case feet and inches), the first thing you need to do is to convert to just one set of units. So, if 1 inch represents 2 feet, that's 1 inch represents 24 inches. So the scale is $1:24$.

Next, you need to know that, to find the ratio of corresponding areas, you will square the numbers in the ratio; and to find the ratio of corresponding volumes you will cube them. Well, it's the volumes that we're dealing with here, so we cube the numbers to get:
Ratio of volumes $= 1^3:24^3$
$=1:13824$
So the actual statue has a volume which is $13824$ times as big as the model. (Sounds a lot, but it's true!)

So if the statue were made of clay, its weight would be $13824\times 1.3$ pounds. But marble is heavier than clay, with the same volume of each in the ratio $175:150$. We can simplify this (by dividing by $25$) to $7:6$.

Therefore the actual weight of the statue is $\frac76\times13824\times1.3$ pounds. And that's about $20966$ pounds, or about $9.36$ tons. It must be quite a large statue!