Three bells are ringing continuously at intervals of $30\min ,36\min ,45\min$ respectively. At what time will they ring again together, if they ring simultaneously at $8 a.m$ is

To find the time when they ring again together, we have to find $L.C.M$ of $30,36,45$.

$L.C.M=5\times 3\times 2\times 3\times 2$

$=180$

The bells will ring together again after $180$ minutes.

The time$180$  minutes $\left(3hrs\right)$ after $8 a.m$.

So bells will ring together again at $11a.m$.