How many stereoisomers does 4-bromopent-2-ene, $\mathrm{CH}{}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CHBr}-\mathrm{CH}{}_3$, have? (Include E/Z isomers and enantiomers.)

There is one stereocentre (C4) giving R and S, and one stereogenic double bond (C2=C3) giving E and Z. The substituents of the molecule are all different, so there is no symmetry and $2\times 2=4$ stereoisomers exist: (2E,4R), (2E,4S), (2Z,4R), (2Z,4S).