Respuesta :

konrad509
[tex]\text{lcm}(20,30,40)=120[/tex]

So, they'll ring together again in 120 minutes.

120 min = 2 h
9:45 + 2:00 = 11:45
The time they will ring together is given by the Lowest Common Multiple of 20, 30 and 40    which is 120 minutes

So  they'll ring together at 9.45 am + 120 minutes

=  9.45 + 2 hours  = 11.45 am Answer