This is false, it is not negative because the answer is 0.
Find multiples of 30 and 40:
30: 30, 60, 90, 120, 150
40: 40, 80, 120, 160
The least common multiple is 120, so every 120 minutes they willl both ring.
1 hour = 60 minutes:
120/60 = 2 hours.
The bells ring together every 2 hours.
8 + 2 = 10 am
10 + = 12pm
12 + 2 = 2 pm
The bells will ring together at am, 12 pm and 2 pm.