The number of all possible combinations of 4 letters which are taken from the letters of the word 'ACCOMMODATION', is

If ${ }^n c_r=c_r$ and $2 \frac{c_1}{c_0}+4 \frac{c_2}{c_1}+6 \frac{c_3}{c_2}+\ldots .+2 n \frac{c_n}{c_{n-1}}=650$, then ${ }^n C_2=$ $\qquad$

The number of odd numbers greater than 600000 that can be formed by using the digits $3,6,7,8,9,0$ without repetition is

There are three sections in a question paper, each section containing 4 questions. If a candidate has to answer only 5 questions from this paper without leaving any section, then the number of ways in which a candidate can make the choice of questions is