Accumulator CPU is example of One Address Instruction:
In Acc. CPU first alu operand is always required in the accumulator but second alu operand can be in the register or memory because of the the availability of the one address along with the opcode.
Load and Store is One address Instruction
X= (M + N x O)/(P x Q)
I1: Load P : ACC<--M[P] //Load the P value from memory to ACCUMULATOR
I2: Mul Q: ACC<--ACC*M[Q] //Second alu operand is in memory and destination is Register
I3: Store T: M[T]<--ACC //Store the Value in memory
I4: Load N : ACC<--M[N]
I5: Mul O : ACC<--ACC*M[O]
I6: Add M: ACC<--ACC+M[M]
I7: Div T: ACC<--ACC/M[T]
I8: Store X: M[X]<--ACC //Finally store in value in memory
TOTAL 8 1 ADDRESS INSTRUCTION REQUIRED.