When four atomic orbitals are mixed to form hybrid orbitals, how many hybrid orbitals are formed?

When four atomic orbitals are mixed to form hybrid orbitals, 4 x sp3 hybrid orbitals are formed.

Carbon's 2s and all three of its 3p orbitals hybridize to form four sp 3 orbitals. These orbitals then bond with four hydrogen atoms through sp 3-s orbital overlap, creating methane.