In this type of problem, a logical circuit diagram will be given. We have to design a Logical circuit from that logical expression.
A logical expression from a logical circuit


A logical expression from a logical circuit

We will find logical gates like AND, OR, NOT, X-OR, X-NOR, NAND, NOR. From these, we have to write proper expressions from each gate output and have to find out a combined output finally.


Logical circuit to logical expression


From here we have to write the expression outputs from each gate. Finally, we will get the final expression for the total circuit.

A and B are inputs of AND gate. So the output is AB. Next, B and C are the input of the OR gate. So the output is B+C. And next these tow are going from a NAND gate. 

In the below C, A is going from AND gate. So the output is A͞C. Finally, both outputs are passing from an OR gate. 

Logical circuit to logical expression

We can simplify the final output if it is in not simplified form.

We know from De Morgan's law,

Ā+ B̄ = A͞B

So the simplification of that expression

Logical circuit to logical expression