Answer:
20 seconds
Step-by-step explanation:
Given the following :
Alarm 1 (goes off every 10 seconds)
Alarm 2 (goes off every 5 seconds)
Alarm 3 (goes off every 4 seconds)
If they all go off now, how long will it take all to go off at the same time again.
Obtain the multiples of the time in seconds in which each alarm goes off and select the lowest multiple common to all three;
Multiples of 10 : 10, 20, 30, 40, 50,...
Multiples of 5 : 5, 10, 15, 20, 25, 30, 35, 40,...
Multiples of 4 : 4, 8, 12, 16, 20, 24, 28, 32, 36,....
Hence, the lowest multiple common to all three alarm times is 20.
Hence, all three alarms will go off at the same time again after 20 seconds
