The number of permutations by taking all letters and keeping the vowels of the word COMBINE in the odd places is

If $${}^{n - 1}{C_3} + {}^{n - 1}{C_4} > {}^n{C_3}$$, then n is just greater than integer

If $${}^n{C_4}$$, $${}^n{C_5}$$ and $${}^n{C_6}$$ are in A.P., then n is

The number of diagonals in a polygon is 20. The number of sides of the polygon is