Four bells begin to toll together at the intervals of 5 second, 6 second, 7 second and 8 second respectively. How many times will they toll together in the span of 2 hours? (Considering that they have tolled once at the start)

Four bells begin to toll together at the intervals of 5 second, 6 second, 7 second and 8 second respectively. How many times will they toll together in the span of 2 hours? (Considering that they have tolled once at the start) Correct Answer 9 times

Given:

Interval of four bells are 5 s, 6 s, 7 s and 8 s

Concept used:

To calculate the intervals of all bells tolling together is to take the L.C.M of the respective intervals.

Calculation:

L.C.M of 5, 6, 7, 8 =

Mistake Points 

Please observe the following two points very carefully to avoid the wrong answer:

(i) We have taken the whole value i.e. 8 in 8.5 because for the next time for the four bells to toll, there are still (0.5 × 14 minutes = 7 minutes left).

(ii) Now, the answer has been taken as 8 + 1 = 9 because we have to also count the tolling when the bells started tolling for the very first time i.e. in the zeroth second.