Question

Four bells begin to toll together at intervals of $6,7,8$ and $9$ seconds. What is the number of times that they will toll together in $2$ hours?

• A. $14$
• B. $15$
• C. $13$
• D. $11$

Answer 1

Answer: (A)

$14$

L. C. M. of $6,7,8,9=504$
$\therefore$ The bells will start ringing after an interval of every $504$ seconds.
Now $2$ hours $=2\times 60\times 60$ seconds $=7200$ seconds
$\therefore$ Number of times the bell will ring in $2$ hours $=\frac{7200}{504}=14.2$ times
Since the bells rang together at the start also therefore the bells will ring 14 times in $2$ hours.