Two identical resistors of 20 Ω each are connected in parallel. This combination, in turn, is connected to a 10 Ω resistor. The equivalent resistance of the combination will be:

R1 = R2 = 20 ohm

R3 = 10 ohm

R1 & R2 are connected in parallel.

Resultant resistance for parallel combination is given by -

$$\frac{1}{R} =\frac{1}{R1} + \frac{1}{R2} $$

$$\frac{1}{R} =\frac{1}{20} + \frac{1}{20} $$

= $$\frac{2}{20} $$

R = 10 ohm

This R and R3 are connected in series.

Equivalent resistance in series combination is given by -

R' = R + R3

R' = 10 + 10

R' = 20 ohm

Equivalent resistance of overall structure is 20 ohm.