I have a exercise like this in my book:

10 balls numbered 0 - 9, removing 4 balls, one by one, I'll have a number.
How many different numbers can I get.

My book has the result as: `10 x 9 x 8 x 7 = 5040`  

But shouldn't it be `9 x 9 x 8 x 7 = 4536`.  

I assumed `0` couldn't be the counted when leftmost.

Is the book solution right? I'm confused.

Thanks.