What is the total resistance of the circuit below?

1/R = 1/2 + 1/3 + 1/1

1/R = 0.5 + 0.333 + 1 = 1.833

R = 1/1.833 = 0.545 Ω

or

1/R = 3/6 + 2/6 + 6/6 = 11/6

R = 6/11 = 0.545  Ω

Here's a test-taking skill, especially if you have limited time!

Parallel is ALWAYS lower than the lowest Resistor, so that eliminates C & D

Estimate with the resistors shown is 1/2 Ω, so a quick guess would be B. 0.55 Ohms, but this only works if the answers have widely spread answers (not 0.5, 0.52, 0.55).

Other people gave you the actual number, I wanted to give you another skill.

Rt = 2//3//1 = 1/(1/2+1/3+1) = 0.545 ohm (rounded up to 0.55)