Question
How to identify the correct folded cardboard house diagram
Original question: 9 The piece of cardboard shown below folds to form a house for use with a model railway. The other side of the cardboard is black, which forms the inside of the house.
Which of the illustrations below correctly shows the assembled house?
A B C D
Expert Verified Solution
Expert intro: These net-folding questions are really about mental rotation and tracking which faces end up inside or outside. The black side detail matters, because it tells you which surfaces are hidden once the house is assembled.
Detailed walkthrough
To choose the correct illustration, trace the cardboard as a net before folding.
What to check
- Which panels become the roof, walls, and base
- Where the black side ends up after the fold
- Which edges meet naturally when the cardboard is bent
How to reason it out
- The side that is black becomes the inside of the house.
- The visible exterior should therefore show the uncolored side.
- Any roof flap must align so that the fold lines connect the walls without reversing the shape.
If an option shows the black side on the outside, it cannot be correct. If an option places the roof or side walls in a way that would require the cardboard to twist instead of fold, it is also wrong.
Because the missing diagram is not included here, the best method is to compare each option against these three checks and eliminate the impossible ones first.
💡 Pitfall guide
A frequent mistake is to focus only on the final shape and ignore the fold lines. Another is forgetting that the opposite side is black, so the inside of the house should not be the same color as the outside.
🔄 Real-world variant
If the cardboard were printed on both sides, the color cue would disappear and you would have to rely entirely on edge matching and symmetry. If one flap were longer than the others, that extra length would usually determine the roof orientation or which wall becomes the front face.
🔍 Related terms
net of a solid, folding diagram, surface orientation
FAQ
How do I decide which folded house diagram is correct?
Track the net edges, identify which panels become the roof and walls, and check that the black side ends up on the inside of the house.
What is the most common mistake on this type of question?
Students often ignore the fold lines or forget that the opposite side is black, so they choose a diagram that places the black surface on the outside.