Problem 5 · 2023 Math Kangaroo
Easy
Logic & Word Problems
careful-counting
Maria switches the lights on and off according to the given plan (the bars show when each of Light 1, Light 2 and Light 3 is on, in minutes). For how many minutes in total are there exactly two lights on at the same time?
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Answer: C — 8
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Hint 1 of 2
Go minute by minute and count how many lights are on.
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Hint 2 of 2
Mark only the minutes where the count is exactly two.
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Approach: scan each minute and tally when exactly two bars overlap
- Read each light's on-intervals from the chart and check every one-minute slot.
- Counting the slots where precisely two of the three bars are present gives 8 such minutes.
- So there are exactly two lights on for 8 minutes.
Mark:
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