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Lesson 7: Volume and surface area word problems

# Volume word problem: gold ring

See if you can find the incremental volume of a ring in cubic inches. You'll need to put to use your knowledge of how to measure volume. Created by Sal Khan.

## Want to join the conversation?

• why would the water move up that amount if there is a hole in the center of the ring? Wouldn't that hole fill up and change the amount of space the water takes up?
• We are interested in the volume of the "gold". The hole in the ring fills up with water but the gold doesn't. So the water displaced by the ring is the volume of the gold
• Wouldn't the volume of the ring be just 0.25 cubic inches? as the ring does not have a length of 3 inches and width of 2 inches?
• The water level rises by 0.25 inches.
If you get 0.25 inches (height added) and multiply it by length and width (2 and 3) You get the total amount of water dispaced, which is the area of the ring. If you multiply your length times your width,(3x2) you get 6. 6 times 0.25 extra height =1.5 or *6 x 0.25 = 1.5
---Hopefully this makes it a little bit easier---
• At , How come the inches in the water increase?
• the ring's volume is 1.5, so it displaces the water so it stays even, Because atoms cant go inside of each other...
• how to find area of box
• A box is a 3D object, so you can either find the volume or the surface area, but there is no such thing as area of a 3D object.
• So, basically, you can find the volume by finding the biggest object, then subtract the space that isn't the smaller object inside, right?
• You take the volume after the item is put in subtract it from what it was before. That is how you get 1.5 cubic inches as the answer.
(1 vote)
• so you can know the ring's volume just like khan said at ?
• Yea dude use the method he taught you in the video.
• I have 2 questions. How could volume be in cubic inches? Why do you need to leave out the '4' in the height when solving for the mass of the ring?
• Couldn't he just, like, find the volume of it by figuring out the volume of a cylinder?

It seems as if he could measure the height of the ring and the radius. Find the volume of that, then find the volume of the HOLLOW part the exact same way but subtracting the 'crust' from the diameter, then subtract? That seems more reasonable to me. Anyone know what I mean??