Problem 20 · 2010 Math Kangaroo
Stretch
Spatial & Visual Reasoning
foldingreflection
A strip of paper is folded three times as shown. Determine β if α = 70°.
Show answer
Answer: C — 120°
Show hints
Hint 1 of 2
Each fold reflects the strip, turning its direction by a fixed amount tied to α.
Still stuck? Show hint 2 →
Hint 2 of 2
Track the running direction of the strip after all three folds.
Show solution
Approach: follow the strip's direction through each reflection
- Folding the strip at angle α = 70° reflects it, changing its heading by the same amount each time.
- After the three folds the two end pieces meet at an angle β.
- Carrying the reflections through gives β = 120°.
Mark:
· log in to save