The options for above question is
a.1 hrs
b.2 hrs
c.3 hrs
d.4 hrs
Logically the next time when they ring together will be a factor(least possible minutes) common to all 3 bellls
so we need to take LCM of 9 ,12 and 15
Calculating from the above steps
LCM = 2 × 2 × 3 × 3 × 1 ×1 × 5 = 180
∴ Time after which the three bells will ring together next = 180 minutes
using formula 60 minutes = 1 hour
∴ 180 minutes = 180 / 60 = 3 hours
the ans is c. 3 hrs
