Question

If R the total resistance for a parrallel cicuit with two resistors of resistance r1 and r2, then 1/R=1/r1+1/r2. Find the resistance, r1, if the total resistance is 20 ohms, and the r2 is 75 ohms. Round if necessary.

Answer 1

You just need to sub in and solve for r1

Answer 2

1/20 = 1/r1 + 1/75

Answer 3

so then 1/-55 = 1/x

Answer 4

No, you don't add fractions like that :P

Answer 5

I see what you did. Bad! You have to remember how to work with fractions.

Answer 6

1/20 - 1/75 = 1/r1

Answer 7

No worries, everyone gets rusty :P.

(1*75)/(20*75) - (1*20)/(20*75) = 1/r1

Answer 8

sorry here are the answers.
A. 16
B. 1405
C. 27
D. 102

Answer 9

they have to have the same denominator in order to add or subtract them. So we just multiply by a factor of one. (1/20 * 75/75)

Answer 10

oh

Answer 11

I'm not gonna do it for ya brah. I gave you the answer essentially, give it a try. You won't learn anything if I give you the answer on a silver platter ;).

Answer 12

I'll let you know if you're wrong

Answer 13

150 is LCD

Answer 14

sorry 200

Answer 15

10/200 - 3/200 = 1r1

Answer 16

is that right

Answer 17

It's not too important to find the LCD, as long as they both have the same denominator

I just did (20*75) to make it easy... in that case I would get 1500 as the Common Denominator.

Answer 18

Look again at what I wrote here: (1*75)/(20*75) - (1*20)/(20*75) = 1/r1

Answer 19

Alternately, if you hate fractions like the plague... you can just switch them to decimals. Use your calculator and find out what 1/20 is, then find out what 1/75 is. Then subtract the two.

Answer 20

1/20 = .05

Answer 21

1/20 - 1/75 = 1/r1
(1*75)/(20*75) - (1*20)/(20*75) = 1/r1
(75 - 20)/1500 = 1/r1
-55/1500 = 1/r1

Answer 22

1/75 =.02

Answer 23

1/20 - 1/75 = 1/r1
(1*75)/(20*75) - (1*20)/(20*75) = 1/r1
(75 - 20)/1500 = 1/r1
55/1500 = 1/r1
r1 = 1500/55 Done

Answer 24

and that is C thanks so much

Answer 25

Work on your fractions man. It's going to be very useful in the parallel circuit stuff of electricity.

Answer 26

Ok will do thanks!!!

Answer 27

I'm glad to help.