For Parallel Circuit, the general formula is:
1/Rt = 1/R1 + 1/R2 + 1/R3 + ….+ 1/Rn where “n” is the number of resistor connected in parallel. This means that the reciprocal of the total resistance is equal to the sum of the reciprocals of the given resistances. For two resistors, 1/Rt = 1/R1 + 1/R2. Simplifying this equation, Rt = (R1*R2)/(R1 + R2). For three resistors in parallel, 1/Rt = 1/R1 + 1/R2 + 1/R3. Also equal to Rt = R1*R2*R3/(R2*R3 + R1*R3 + R1*R2). And so on…