A perfect _______number can never have the digit $7$ at the unit's place ______.

The least number which when subtracted from $1850$ makes it a perfect square, is:

$\frac{4.2\times 4.2-1.9\times 1.9}{2.3\times 6.1}$ is equal to:

Three-fifth of the square of a certain number is $126.15$ What is the number?

The least perfect square number divisible by each one of $3,4,5,6,8$ is:

The least number to be added to $269$ to make it a perfect square is:

The largest number of five-digit when it is a perfect square, is: