The CH3 protons produce a peak at δ 1.8 but, instead of a single peak, a triplet is produced. This is because the CH3 protons couple with the adjacent two CH2 protons.
The CH2 protons produce a peak at δ 3.2 but, instead of a single peak, a quartet is produced. This is because the CH2 protons couple with the adjacent three CH3protons.
In general, if there are 'n' protons three bonds away from the resonating group, the absorption will be split into a multiplet of n+1 lines.
