[D′+AB′+A′C+AC′D+A′C′D]′
=[D′+AC′D+AB′+A′C+A′C′D]′
=[D′+AC′+AB′+A′[C+C′D]]′
=[D′+AC′+AB′+A′[C+D]]′
=[D′+AC′+AB′+A′C+A′D]′
∵ (D′+A′D=D′+A′)
=[D′+A′+AC′+AB′+A′C]′
∵ A′+A′C+=A′
∵ A′+AC′+AB′=A′+A(C′+B′)=A′+C′+B′
=[D′+A′+C′+B′]′
=ABCD
Hence, only 1 minterm is required.