Answer:
C 3.33 Ω
Explanation:
From the equation given 1 / Rtot = 1/10 + 1/5 = 3/10
then Rtot = 10/3 = 3.33 Ω
As an aside:
When there are only two resistors in parallel, the equivalent R is
= R1*R2 / (R1 + R2) = 10*5 / (10+5) = 50 / 15 = 3.33 Ω
