Problem 9 · 2014 Math Kangaroo
Medium
Arithmetic & Operations
careful-counting
The little witch takes part in a broomstick flying competition of 5 rounds. The times at which she crossed the starting line are shown in the table. Which round was her fastest?
| Time | |
|---|---|
| Start | 09:55 |
| after round 1 | 10:26 |
| after round 2 | 10:54 |
| after round 3 | 11:28 |
| after round 4 | 12:03 |
| after round 5 | 12:32 |
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Answer: B — the second
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Hint 1 of 2
A round's time is the gap between two crossing times, not the clock time itself.
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Hint 2 of 2
Subtract each crossing time from the previous one and look for the smallest gap.
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Approach: find each round's length as a time gap and pick the smallest
- Round 1 lasted 09:55 to 10:26 = 31 min; Round 2: 10:26 to 10:54 = 28 min; Round 3: 10:54 to 11:28 = 34 min; Round 4: 11:28 to 12:03 = 35 min; Round 5: 12:03 to 12:32 = 29 min.
- The shortest gap is 28 minutes.
- That is Round 2, so the fastest round was the second.
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