Question

Find two natural numbers in ratio $5:7$ such that their $lcm$ is $210$.

Answer 1

Let the two numbers be $5x$ and $7x$.

Now LC.M. of $5x$ and $7x$ is $210$.

Therefore,

$5\times 7\times x=210$

$\Rightarrow x=\frac{210}{35}=6$

Hence the required numbers are $30$ and $42$.