$\pi$ is a . . . . . . type of number. (Rational,Irrational,Whole number)

Any odd positive integer $a$ is of the form . . . . . . ,where $m$ is an integer.

Find the $HCF$ of $12$,$15$,and $21$.

The last digit of $2^{3} \times 5^{125}$ is . . . . . . .

Explain why $7 \times 11 \times 13 + 13$ and $7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1 + 5$ are composite numbers.

The last digit of $5^{25}$ is .......