# Missing resistor parallel circuit

#### JuggernautJB

Joined Oct 17, 2017
2
Trying to figure out the missing resistor in a parallel circut

R1= 20
R2=?
Rt= 13.33

Any help would be great

#### dl324

Joined Mar 30, 2015
11,264
Welcome to AAC!

In homework help, you need to show your best effort so we can see where you're having difficulty.

#### philba

Joined Aug 17, 2017
960
Write out the equation for parallel resistance. Then, manipulate the equation to isolate R2.

#### JuggernautJB

Joined Oct 17, 2017
2
Write out the equation for parallel resistance. Then, manipulate the equation to isolate R2.
Thanks. Was trying to figure out the equation

#### philba

Joined Aug 17, 2017
960
It's just simple algebra. Practice it until you can do it in your sleep.

#### dl324

Joined Mar 30, 2015
11,264
Was trying to figure out the equation
For calculating the resistance of two resistors in parallel?

#### WBahn

Joined Mar 31, 2012
26,064
Thanks. Was trying to figure out the equation
So show your work. Maybe we can help. What is your starting point? If you have known values for R1 and R2, how would you calculate Rt? Start with that formula.

Also, see if you can place some limits on what the value of R2 can be? What would Rt be if R2 was 20 Ω? Based on that, does R2 need to be more or less than 20 Ω. This will help you catch wrong answers instead of just blindly accepting them.

#### shteii01

Joined Feb 19, 2010
4,644
It goes something like this: