any noise will pass straight through to the ADC subsystem, introducing measurement error. You have two choices to mitigate this: SW filtering and HW filtering. Either way around, you need a HW anti-aliasing (low pass) filter following the output.
Assume the uC sample rate, Fs, is 100 Hz with 8 bit resolution.
1.what is the value of 1 LSB referred to 3 V ?
2.what is the maximum allowable (Nyquist) frequency FN your system can sample without aliasing ?
3.How much attenuation must your filter have in order to reject frequencies above Fs ? This annenuation is Amin (Hint: it is related to the value of 1 LSB)
4.what order must your filter be to achieve these goals if we pick Fo = Fs/4 (25 Hz) ? (-3db is Fo and your attenuation Amin occurs at Fs)