One light flashes every seconds and another every seconds. They flash together at time . After how many seconds do they next flash together?
Answer and explanation
Correct answer: D. 60 seconds
- Step 1: Find the lowest common multiple of and .
- Step 2: Multiples of : . Multiples of : .
- Step 3: The first common multiple is .
Answer
60 seconds.
Why not the others: 4 seconds: This is the highest common factor, not the lowest common multiple. 240 seconds: This is , a common multiple but not the lowest. 32 seconds: This adds the two times together.
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