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Four devices give signals at intervals of (28), (36), (63), and (84) seconds respectively. They signal together now. After how many seconds will they signal together again?
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Answer and explanation
Correct answer: (252)
Step 1: The next common signal time is the LCM of all intervals. Step 2: (28=2^2\times7), (36=2^2\times3^2), (63=3^2\times7), and (84=2^2\times3\times7), so the LCM is (252). Step 3: Use LCM for repeated-time questions.
Frequently asked questions
What is the correct answer to this question?
(252)
Why is this the correct answer?
Step 1: The next common signal time is the LCM of all intervals. Step 2: (28=2^2\times7), (36=2^2\times3^2), (63=3^2\times7), and (84=2^2\times3\times7), so the LCM is (252). Step 3: Use LCM for repeated-time questions.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Real Numbers. Topic: HCF and LCM using prime factorisation.
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