The total number of rational terms in the expansion of $\left(7^{\frac 13} + 11^{\frac 19}\right)^{6561}$ is

The coefficient of middle term in the expansion of $(1+{x})^{40}$ is

The number of irrational terms in the expansion of$( \sqrt [ 8 ] { 5 } + \sqrt [ 6 ] { 2 } ) ^ { 100 } ,$ is

In the expansion of $(a-b)^{n},n\ge 5$, if the sum of the $5^{th}$ and $6^{th}$ terms is zero, then $a/b$=

The term independent of $x$ in the expansion of $\left [\sqrt {\dfrac {x}{3}} + \sqrt {\dfrac {3}{2x^{2}}} \right ]^{10}$ is