The number of all numbers having 5 digits, with distinct digits is

Out of 7 consonants and 4 vowels, words are formed each having 3 consonants and 2 vowels. The number of such words that can be formed is

If $${1 \over {{}^5{C_r}}} + {1 \over {{}^6{C_r}}} = {1 \over {{}^4{C_r}}}$$, then the value of r is

If $${}^n{C_{r - 1}} = 36,{}^n{C_r} = 84$$ and $${}^n{C_{r + 1}} = 126$$, then the value of $${}^n{C_8}$$ is