  We report ultra-low temperature experiments on the obscure fractional quantum
Hall effect (FQHE) at Landau level filling factor $\nu$=5/2 in a very high
mobility specimen of $\mu=1.7 \times 10^7$ cm$^2$/Vs. We achieve an electron
temperature as low as $\sim$ 4~mK, where we observe vanishing $R_{xx}$ and, for
the first time, a quantized Hall resistance, $R_{xy}=h/(5/2e^2)$ to within 2
ppm. $R_{xy}$ at the neighboring odd-denominator states $\nu$=7/3 and 8/3 is
also quantized. The temperature dependences of the $R_{xx}$-minima at these
fractional fillings yield activation energy gaps $\Delta_{5/2}$=0.11K,
$\Delta_{7/3}$=0.10K, and $\Delta_{8/3}$=0.055K.
