of equal resistance

• Feb 27th 2008, 11:35 AM
lovinhockey26
of equal resistance
What resistance must be placed in parallel with a 149 Ohm resistor to make the equivalent resistance 124 Ohm?
• Feb 27th 2008, 11:41 AM
Peritus
• Feb 27th 2008, 11:49 AM
lovinhockey26
I'm still not sure what I need to use...
I'm not really adding the resistance... I'm trying to find the resistance necessary to be placed parallel to make the equivalence resistance 124 ohm...

still confused i guess...
• Feb 27th 2008, 12:43 PM
Aryth
Well, we use the formula for parallel resistors to find the equivalent resistance for two resistors:

$\displaystyle \text{We have the following information: }$

$\displaystyle R_1 = 149 \Omega$

$\displaystyle R_{Total} = 124 \Omega$

$\displaystyle \text{The Equation is: }$

$\displaystyle \frac{1}{R_{Total}} = \frac{1}{R_1} + \frac{1}{R_2}$

$\displaystyle \frac{1}{124} = \frac{1}{149} + \frac{1}{R_2}$

$\displaystyle \frac{1}{124} - \frac{1}{149} = \frac{1}{R_2}$

$\displaystyle \frac{149}{18476} - \frac{124}{18476} = \frac{1}{R_2}$

$\displaystyle \frac{25}{18476} = \frac{1}{R_2}$

$\displaystyle R_2*\frac{25}{18476} = 1$

$\displaystyle 25R_2 = 18476$

$\displaystyle R_2 = \frac{18476}{25}$

$\displaystyle R_2 = 739.04 \Omega$

And there you go.
• Feb 28th 2008, 09:36 AM
lovinhockey26
you have been very helpful, I appreciate your knowledge and assistance beyond what I can express..

Thank you :)