Series-Parallel Circuits - Engineering

Q1:

Two 1.2 k resistors are in series and this series combination is in parallel with a 3.3 k resistor. The total resistance is

A 138 

B 1,389 

C 5,700 

D 880 

ANS:B - 1,389 

Two resistors are in series.
1.2K ohm and 1.2K ohm.
Total Resistance in Series r=R1+R2=>1.2K ohm+1.2K ohm=2.4K ohm.

Then that is parrallel with 3.3K ohm.

Total resistance in Parallel=1/R=1/r+1/R3.

1/R=(1/2.4K ohm)+(1/3.3K ohm)=>R=1389.47 ohm.