In how many ways can a student choose a programme of $5$ courses if $9$ courses are available and $2$ specific courses are compulsory for every student?
There are $9$ courses available out of which, $2$ specific courses are compulsory for every student.
Therefore, every student has to choose $3$ courses out of the remaining $7$ courses. This can be chosen in $^{7} C_{3}$ ways.
Thus, required number of ways of choosing the programme
$=\,^{7} C_{3}=\frac{7 !}{3 ! 4 !}=\frac{7 \times 6 \times 5 \times 4 !}{3 \times 2 \times 1 \times 4 !}=35$
In how many ways can $5$ red and $4$ white balls be drawn from a bag containing $10$ red and $8$ white balls
The number of ways, in which $5$ girls and $7$ boys can be seated at a round table so that no two girls sit together, is
The number of ways in which we can select three numbers from $1$ to $30$ so as to exclude every selection of all even numbers is
$^{n - 1}{C_r} = ({k^2} - 3)\,.{\,^n}{C_{r + 1}}$ if $k \in $
If $\sum\limits_{i = 0}^4 {^{4 + 1}} {C_i} + \sum\limits_{j = 6}^9 {^{3 + j}} {C_j} = {\,^x}{C_y}$ ($x$ is prime number), then which one of the following is incorrect