My son Nick only has 24.
At age ten it is very possible to have lost all of the baby teeth. There are a total of 20 baby teeth (2 molars, 2 premolars, 2 canines, 2 lateral incisors, and 2 central incisors). It is also possible to not have lost many of the teeth as well. Every childs body is different. Sometimes it is suggested that the teeth are extracted so as to allow the adult teeth to erupt.
I'm guessing 29. Probably more, but my guess. I have lost almost 12 teeth, so I think I should know.