(a) Here both resistance i.e. R₁ = 500 ohm, R₂ = 1000 ohm are connected in series

So equivalent resistance R = R₁ + R₂ = 500 + 1000 = 1500ohm.

(b) Here both resistance i.e. R₁=2ohm, R₂=2ohm are connected in parallel

So equivalent resistance

1/R=1/R₁+1/R₂

1/R=1/2+1/2

R=1ohm

(c) Here resistance R₁=4ohm and R₂=4ohm are in parallel and R₃=3ohm are in series

According to the given figure,

1/R=1/R₁+1/R₂

1/R=1/4+1/4

R=2ohm

Total resistance of the given circuit =R+R₃

=2+3=5ohm