Question

LCM of two numbers x and y is $720$ and the LCM of numbers $12x$ and $5y$ is also$720$.The number y is

• A. $180$
• B. $144$
• C. $120$
• D. $90$

Answer 1

The correct option is B $144$

Given :

LCM of $x$ and $y$ is $720$.

Also, LCM of $12x$ and $5y$ is 720.

$⟹$ $12$ is one of the factor of $y$ and $5$ is one of the factor of $x$.

$5\times 12=60$, so we need only $12$ to get the LCM as $720$.

$\therefore$ $12$ is another factor of both $x$ and $y$

$⟹$ $x=12\times 5=60$ and $y=12\times 12=144$

And $12x,5y$ has LCM $720$.

Hence, $y=144$.