Discussion
A planar rectangular paper has two V-shaped pieces attached as shown below.
This piece of paper is folded to make the following closed three-dimensional object.
The number of folds required to form the above object is
Answer: A
The object needs 9 folds.
The closed V-shaped object is a prism whose cross-section is the outline of the V. Following the drawing, that outline has 8 sides: the two outer slanted walls, the flat outer bottom, the two inner slanted walls, the small flat inner bottom, and the flat top of each arm.
The long rectangular strip wraps around the V to form these 8 walls. Eight walls in a row need a fold between each neighbouring pair, 7 folds; the last wall meets the first at a joint where the strip's two ends come together, which is a seam, not a fold. The two V-shaped pieces are the end caps, and each is folded once along the edge where it is attached: 2 more folds.
That gives 7 + 2 = 9. 7 counts only the strip, 8 adds just one cap, and 11 counts extra folds the design does not need.
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