Answer
$6840$
Work Step by Step
Write the correct form as below:
We know that $n!=1 \cdot 2 \cdot 3 .....(n-1)n$
Thus, we have $\dfrac{20!}{(20-3)}=\dfrac{20 !}{17 !}$
$=\dfrac{20 \cdot 19 \cdot 18 \cdot 17 \cdot 16 \cdot 15 \cdot 14 \cdot 13 \cdot 12 \cdot 11 \cdot 10 \cdot 9\cdot 8 \cdot 7 \cdot 6 \cdot 5 \cdot 4 \cdot 3 \cdot 2 \cdot 1}{17 !}$
$=20 \cdot 19 \cdot 18$
$=6840$
