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Four different electronic devices make a beep after every 30 minutes, 1 hour, 1.5 hour and 1 hour 45 minutes respectively. All the devices beeped together at 12 noon. They will again beep together at:

Answer:

Explanation:

In this example, we have 30, 60, 90 and 105.
The LCM (30, 60, 90, 105) would be:
30 = 2 * 3 * 5
60 = 2 * 2 * 3 * 5
90 = 2 * 3 * 3 * 5
105 = 3 * 35 or 3 * 5 * 7
The final equation would be : (2 * 2) * (3 * 3) * 5 * 7 = 1260
1260 Minutes / 60 = 21 hours.
If all devices beeped initially at 12 Noon, based on our calculation, next time each device will beep simultaneously will be at 9AM the next day