Question

Four mobile phones commence vibrating together and vibrate at an intervals of $16,9,8$ and $4$ seconds respectively. In $12$ minutes, how many times will they vibrate together.

• A. $7$
• B. $4$
• C. $5$
• D. $Noneofthese$

Answer 1

The correct option is C $5$

Given intervals $16,9,8,4$

So $LCM$ of $16,9,8,4$ is

Ref image

$2\times 2\times 4\times 9=144$

They will vibrate $144$ seconds together

So in $12$ min i.e $12\times 60=720$

i.e; $\frac{720}{144}=5$