How to get the equivalent resistance in this figure
-----------r2-------
| | |
Battery. R1 R3
| | |
-----------R4------
Values:
R1= 90
R2= 50
R3= 40
R4= 20
I will guess that you mean the current leaves the battery and runs through r2
then splits and runs through r1 and r3 in parallel
then joins again and runs through r4 back to the battery.
If I guess right then
r1 and r =3 in parallel are
r1 r3 /(r1+r3) = 90*40/(130)
= 3600/130 = 27.7
then total is
50+27.7+20