Answer
900
Work Step by Step
See p.709:
If $n$ is a positive integer, the notation $n!$ (read $n$ factorial'') is the product of all positive integers from $n$ down through 1.
$n!=n(n-1)(n-2)\cdots(3)(2)(1)$
Note: $0!$ (zero factorial), by definition, is 1.
$0!=1$
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$(n+1)!$ os obtained by multiplying $n!$ with $(n+1).$
So, write
$\displaystyle \frac{900!}{899!}=\frac{900\cdot 899!}{899!}$
...and reduce the fraction...
$=900$
