Physics
posted by Jason .
Comicstrip hero Superman meets an asteroid in outer space, and hurls it at 750 m/s, as fast as a bullet. The asteroid is three thousand times more massive than Superman. In the strip, Superman is seen at rest after the throw. Taking physics into account, what would be his recoil velocity?

His momentum would have to equal that of the asteroid, but in the opposite direction. That would require that
V(superman) = 3000*750 m/s = 2.25*10^6 m/s
which is about 1% of the speed of light. 
Where do you get 10^6 m/s?
So is the answer 22.5 or 225,000,000 
No, it is neither of those two numbers you wrote.
It is what it is.
Do the multiplication.