Examples for single displacement reactions:
Zn (s) + CuSo4 (aq) -> ZnSO4 + Cu
2Al + 3CuSO4 -> 3Cu + Al2(SO4)3
The idea for single displacement is:
A + BC -> AC + B
In this case:
ЗKOH + H3PO4 --> K3PO4 + 3H2O
We see a double displacement, where K goes to H3PO4 and the H goes to OH to form H2O
AB + CD -> AC + BD