The ratio of two numbers is $3:4$ and their $HCF$ is $4$. Their $LCM$ is

$A$ heap of stones can be made up into groups of $21$. When made up into groups of $16, 20, 25$ and $45$,there are $3$ stones left in each case. How many stones at least can there be in the heap?

The $LCM$ of two numbers is $495$ and their $HCF$ is $5.$ If the sum of the numbers is $100,$ then their difference is

What will be the least number which when doubled will be exactly divisible by $12, 18, 21$ and $30$?

There are five bells which start ringing together at intervals of $3, 6, 9, 12$ and $15$ seconds respectively. In $36$ minutes,how many times will the bells ring simultaneously?

Find the greatest number which exactly divides $200$ and $320$.