Problem 9 · 2009 Math Kangaroo
Medium
Ratios, Rates & Proportions
proportion
A bridge is being built across a river that is 120 m wide. One quarter of the bridge continues onto the land on the left bank, and another quarter continues onto the land on the right bank. How long is the bridge?
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Answer: D — 240 m
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Hint 1 of 2
A quarter on each bank means half the bridge is over the water.
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Hint 2 of 2
If the river part is half the bridge and equals 120 m, scale up.
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Approach: part-to-whole
- One quarter is on the left land and one quarter on the right land, so half the bridge is over the river.
- That river half is 120 m.
- So the whole bridge is 2 × 120 = 240 m — answer D.
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