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### Course: 7th grade foundations (Eureka Math/EngageNY)>Unit 6

Lesson 3: Topic D: Foundations

# Surface area of a box using nets

Discover the surface area of a cereal box by visualizing a net. Cut and flatten the box to create a 2D shape. Measure the dimensions, calculate the area of each section, and add them up for the total surface area. Fun and practical!

## Want to join the conversation?

• You don't have to use a net. S=2lw+2wh+2lh
• Or 2(lw+wh+lh)
• At is he drawing in the height?
• Sort of, he is drawing what cannot be seen, the height of the back of the cereal box. Dotted lines mean behind the shape.
• this is hard can some one help
• If you find this method hard, try the previous video.
Or use the formula 2(lb+bh+lh)
where l is length , b is breadth and h is height.
• Sal is the best. Khan academy videos are ta best
• You should write this post in the Tips and Thanks section.
• Ok, here's a question. Why do we need the use of nets in real life? Is it just the standard they added to extend school? BTW: Sal makes me want to learn more about cereal boxes and math :-)
• Most boxes are flat when they are produced, think of pizza boxes, the ppl at the pizza shops fold the boxes. They need to know the dimensions to order the proper sizes.

When building Wood Framed Structures usually the walls are made on the ground first then lifted up into position. so the "net" is made first before the building takes shape
(1 vote)
• Why can’t you just multiply height times width times base?
• If you multiply these three, you are finding the volume, not surface area.
• I don't know how to break it up
• There are many ways to break up a box into a net. Just think of a way to unfold the box flat onto a surface. It might take a little bit of practice.
• do these types of methods also work in real life?
• If you want to find a way to break down boxes in a cool way then yes.

If you mean volume then that is very important in life. If you get a package that has a volume of 20 ft^3 or something, then what's in there has to be kinda big, heavy, or fragile because you would also need the wrapping to protect it if it's glass or whatever

So to answer your question, yes. If you mean geometry in general then that's also "Yes".
• How do you do this again
• Imagine that you are unfolding a polyhedron to be flat.

It might help to draw what that looks like, you might need to practice a few times, but you should get a hang of it.

After you have the net of your polyhedron, then find the area by breaking it down into shapes that you know how to take the area of, such as rectangles and triangles.

Then, add the total area together to get your answer, which is equal to the surface area of the polyhedron.