To answer this question, one needs to invoke Hume's argument against miracles.
"No testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous than the fact which it endeavors to establish."
The existence of someone else is not an extraordinary claim. Given the information (evidence) available for deducing the existence of other human beings, the claim that other human beings exist is "of such a kind, that its falsehood would be more miraculous than the fact which it endeavors to establish."
Of course, this does not prove other human beings exist, it only deduces that the belief that they do is very reasonable, and the disbelief very unreasonable. No one can prove anything 100% unless they are omniscient, but if showing this is the point of your question then asking it is the same as asking nothing at all. In remembrance of Karl Popper, who said "A theory which explains everything explains nothing", someone who says something so obvious is better off not having wasted his breath.
As an aside, I loathe the types who will say something like "How do you know the chair you're sitting in is real?" and think they've just asked something totally mind-blowing and revolutionary. Ever notice that many of these types who say they like to think "deep" are really only conducting "murky thought"? Some people just need to be slapped.