Four chimes ring simultaneously at 5:30 a.m. After that, they ring at the intervals of 15 seconds, 20 seconds, 25 seconds and 30 seconds, respectively. How many times will these chimes ring together till 8:15 a.m., including at 5:30 a.m.?

Correct option is B

​Given:

Four chimes ring together at 5:30 a.m.

Intervals: 15 s, 20 s, 25 s, and 30 s

We are to count how many times they ring together from 5:30 a.m. to 8:15 a.m. (inclusive)

Solution:

LCM of 15, 20, 25, 30 = 300 seconds

Time from 5:30 a.m. to 8:15 a.m. = 2 hours 45 minutes

= 165 × 60 =  9900 seconds

Number of times(including 5 : 30 am)

​$$= \frac{9900}{300} + 1 = 33 + 1 = 34$$​​

Thus, The chimes will ring together 34 times