# Maths Playing With Numbers part 38 (Questions 3) CBSE Class 6 Mathematics VI | Summary and Q&A

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August 31, 2016
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LearnoHub - Class 11, 12
Maths Playing With Numbers part 38 (Questions 3) CBSE Class 6 Mathematics VI

## TL;DR

This video explains how to find the next time at which three traffic lights will change simultaneously using the concept of least common multiple (LCM).

## Key Insights

• 💱 Simultaneous changes in events can be determined using the concept of least common multiple (LCM).
• 🧑‍🏭 Calculating LCM involves finding the product of unique prime factors of the given numbers.
• ❓ The LCM provides the minimum value at which events will align again.
• ✋ Understanding the question is crucial in choosing between LCM and highest common factor (HCF) and determining the appropriate value (greatest or least) to be calculated.
• 🧑‍🏭 Regular practice with problems involving factors, multiples, prime factorization, HCF, and LCM is necessary to strengthen understanding and application in real-world scenarios.
• 🥶 ExamFeel.com offers free educational resources, including video lessons, notes, and online tests, for subjects like physics, chemistry, mathematics, and biology for students in grades 6 to 12.

## Transcript

hello friends this video on playing with numbers part 38 is brought to you by exam feel calm know who fear from exam question number five the traffic lights at three different road crossings change after every forty eight seconds seventy two seconds and one hundred eight seconds respectively if the change simultaneously at 7 a.m. at what time will ... Read More

### Q: How can we determine the next time at which the traffic lights will change together?

We can find the next time by calculating the least common multiple (LCM) of the intervals between the light changes. In this case, the LCM is 432 seconds or 7.2 minutes from the initial change at 7 a.m.

### Q: What is the significance of finding the least common multiple?

The LCM helps us identify the minimum value at which the traffic lights will change simultaneously again. It is necessary to ensure all three intervals are satisfied, as they could have additional common multiples.

### Q: Should we always calculate the LCM for finding simultaneous events?

Calculating the LCM is necessary when the events occur at different intervals and need to align simultaneously. It ensures accuracy in determining the next occurrence for various scenarios, such as the traffic lights problem discussed.

### Q: Why is it important to understand the question and the goal before using LCM or HCF?

Understanding the question helps in identifying whether we need to find the common multiple or common factors. It also helps determine whether the solution requires the greatest or least value of the common multiple, leading to the appropriate use of LCM or HCF.

## Summary & Key Takeaways

• The video introduces a problem where three traffic lights change at different intervals: 48 seconds, 72 seconds, and 108 seconds.

• The objective is to determine the next time at which all three traffic lights will change simultaneously.

• By finding the least common multiple (LCM) of the intervals, the video calculates that the lights will change again after 7.2 minutes or approximately 7 minutes after the initial change.