Problem 14 · 2018 Math Kangaroo
Stretch
Geometry & Measurement
spatial-reasoning
Susi makes this pattern using ice-lolly sticks. Each stick is 5 cm long and 1 cm wide. How long is Susi's pattern?
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Answer: B — 21 cm
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Hint 1 of 3
Look only at how far the pattern reaches from left to right — that is its length.
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Hint 2 of 3
Along that length, five 5 cm sticks reach across, but they cross each other and overlap.
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Hint 3 of 3
Each place two sticks overlap, they share 1 cm (the width of a stick), so that 1 cm only counts once.
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Approach: add the stick lengths along the row, then subtract the overlaps
- Measure the pattern left to right: five 5 cm sticks reach across its length, which alone would be 5 × 5 = 25 cm.
- But the sticks cross and overlap at 4 places, and each overlap is 1 cm wide (a stick's width), so 4 cm is counted twice.
- Take those 4 cm away once: 25 − 4 = 21 cm.
Mark:
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