Six bells commence tolling together and toll at intervals of 2, 4, 6, 8, 10 and 12 seconds respectively. In 30 minutes , how many times do they toll together ?

Answer: Option D

LCM of 2, 4, 6, 8, 10, 12 is 120
So the bells will toll together after every 120 seconds, i.e., 2 minutes
In 30 minutes, they will toll together
$$\begin{array}{rl}& =\left[\left(\frac{30}{2}\right)+1\right]\\ & =\text{16 times}\end{array}$$