I'm assuming you meant "even and odd". Yes, the sampling frequency is 200 kHz for the downsampled by 2 data.
Fs = 400e3;
t = 0:1/Fs:1;
x = cos(2*pi*50e3*t);
xeven = x(1:2:end);
xodd = x(2:2:end);
xeven_dft = fft(xeven);
xodd_dft = fft(xodd);