A child studies an unfolded marked paper shape with several possible crease directions.
a fold-test mystery

Which crease pairs every mark?

mission started — every mark needs a twin

A shape may look balanced until one mark has no twin. Learn the fold test, then check a brand-new pattern.

clue 1

A fold compares two sides

The same child begins folding one completely plain sheet along a simple practice crease.

A reflection fold pairs every point with a twin the same perpendicular distance across one line.

clue 2 · equal distance

Slide a point; its twin follows

low pairpaired at center
low pairhigh pair

Move one point beside a practice crease. Its reflected twin stays equally far on the other side and at the same height.

clue 3 · check every point

The outline is not enough

pattern Avertical practice axis works
pattern Apattern C

Try three unrelated patterns. A proposed axis works only if every mark has a reflected partner.

try the test

Fold marks onto their partners

openpractice sheet open
openclosed

Close a simple vertical practice fold. Matching marks land together; one missing twin would remain exposed.

put the clues together

A new pattern, three fair choices

Vertical, horizontal, and upper-left-to-lower-right diagonal creases use the same color and weight. Check every mark, not just the outside box.

Commit before the new setup runs.

Which fold line makes EVERY mark land on a twin?