A  number divisible by $2$ is an even number.

 Sum of two odd prime numbers is always _____ .

If $\frac{72}{198}=\frac{k}{11}$ then $k=$ _____.

If the LCM of $2^3, 2^2\times 3, 2\times 3^2$ in exponential form is $2^a\times 3^b$ then find $a+b$.

_____

 The product of two numbers is $640$. If the HCF is $16$ then the LCM is _____ .