For any positive integer $n$,the last digit of $5^n$ is always.......

The product of any four consecutive positive integers is always divisible by . . . . . . .

If $m$ and $n$ are distinct prime integers,then their $HCF$ is .......... .

For two consecutive positive integers $a$ and $b$,what is the value of $\text{HCF}(a, b) \times \text{LCM}(a, b)$?

What is the remainder when $27$ is divided by $4$?

Which of the following is a rational number?