Question

three alarm clocks ring at intervals of 4,12 and 20 minutes respectively. if start ringing together, after how much time will they next ring together?

Answer 1

4,12,20

2=4,12,20
2= 2,6,10
3=1,3,5
5=1,1 ,5
1,1,1

,lcm=2*2*3*5=60 so after60 min after the alarm clock ring

Answer 2

They will ring for 1 hour

Step-by-step explanation:

All the alarm clocks will ring together after the number of minutes which are least common to all the three.

LCM of all the three is as follows:

2 |4, 12, 20|

2 |2, 6, 10|

   |1, 3, 5|

$L C M=2 \times 2 \times 3 \times 5=60 \text { minutes }=1 \ \text{hour}$

After 1 hour, all the three clocks will ring together.