Question

four bells commence tolling together . They toll at intervals of 1, 11/4,11/2,13/4 seconds. After what intervals will they toll again.

Answer 1

to simplify calculation lets make the denominator same
so now we have 
4/4
11/4
22/4 and 
13/4

LCM of 4,11,22,13 is 572

so the bells will rang together after 572/4 seconds i.e after 143 seconds

Answer 2

Answer: 2 minute 23 seconds.

Step-by-step explanation:

bells toll at intervals of 1, 11/4,11/2,13/4 seconds.

they will toll again after,

L.C.M. of ( 1, 11/4,11/2,13/4 seconds. )

to simplify calculation lets make the denominator equal.

so now we have

4/4, 11/4, 22/4 and 13/4

LCM of 4,11,22,13 is 572

so the bells will rang together after 572/4 seconds i.e after 143 seconds or 2 minute 23 seconds.