Parallel resistors (3)
Special case for just two resistors in parallel,

When two resistors are in parallel, the equivalent resistance is the product of the two resistors divided by their sum.

When the two resistors have the same value, the equivalent parallel resistance is exactly half of the original resistance.
Created by Willy McAllister.
Parallel resistors simulation model
 Compute the equivalent parallel resistor using the formula from this video,
$\qquad\text R_\text{equiv} = \dfrac{\text R1\,\text R2}{\text R1 + \text R2}$
 Find the current in the equivalent resistor,
$\qquad i = \text V1/\text R_\text{equiv}$

Click on DC to see what the simulator thinks. Compare your answers.
 Make the two resistors the same value.
 Compute the equivalent parallel resistor in your head. Change $\text R_\text{equiv}$ to that value.
 Compute the current in the equivalent resistor in your head.
 Click on DC to simulate. Compare your answers.