$\"\"$

The number of combinations of n distinct objects taken r at a time given by $\"\"$ .

The expression is $\"\"$ .

$\"\"$ (Apply Combination formula)

$\"\"$ (Substitute $\"\"$ )

$\"\"$ (Subtract: $\"\"$ ) $\"\"$

Expand the factorial: $\"\"$ .

$\"\"$

$\"\"$ (Cancel common terms)

$\"\"$ (Multiply: $\"\"$ )

$\"\"$ (Divide: $\"\"$ ) $\"\"$

The value of $\"\"$ is 10.