One atomic mass unit is equal to?

(Given, mass of one carbon-12 atom $=1.992\times 10^{-23}$)

One atomic mass unit (amu or u) is equal to 1/12th of the mass of an atom of carbon-12. 

Mass of an atom of carbon-12 $=1.992\times 10^{-23}g$

1 amu $=$ 1/12 mass of carbon-12 atom $=\frac{1}{12}\times 1.992\times 10^{-23}$ $=1.66\times 10^{-24}g$