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#### bigbenny

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Discussion Starter · ·
Anybody here good with math and formulas? I have a problem I can't get past.

What is the total resistance of this circuit?

1/R = 1/6.25 + 1/7.5

Also, can you list step by step on how you figured this out?

Thanks a ton :thumbup:

#### Dennis Alwon

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Retired EC
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24,339 Posts
Anybody here good with math and formulas? I have a problem I can't get past.

What is the total resistance of this circuit?

1/R = 1/6.25 + 1/7.5

Also, can you list step by step on how you figured this out?

Thanks a ton :thumbup:
1/R=1/6.25 + 1/7.5

1/R= .16 + .133 = .293

1/R= .293

Multiply both side by R

1= .293 x R

divide both sides by .293

1/.293 = R

3.41= R

#### Tsmil

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742 Posts
You are using a calculator, right?

#### dmxtothemax

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Anybody here good with math and formulas? I have a problem I can't get past.

What is the total resistance of this circuit?

1/R = 1/6.25 + 1/7.5

Also, can you list step by step on how you figured this out?

Thanks a ton :thumbup:
If those two resistors are in parrallel
I.E. 6.25 & 7.5
then its 3.44 ohms.

1/6.25 = .16

1/7.5 = .13

.16 + .13 = .29

1/.29 = 3.44

#### five.five-six

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Anybody here good with math and formulas? I have a problem I can't get past.

What is the total resistance of this circuit?

1/R = 1/6.25 + 1/7.5

Also, can you list step by step on how you figured this out?

Thanks a ton :thumbup:
This is for a parallel circuit, A good little "check sum" is that your solution will be less than any of your individual resistances. If you come up with a number larger than any of your original resistance values you have done something wrong.

#### five.five-six

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You are using a calculator, right?
Dennis doesn't use a calculator, Dennis is a calculator!

#### wildleg

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##### animal lover /rat bastard
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13,543 Posts
Anybody here good with math and formulas? I have a problem I can't get past.

What is the total resistance of this circuit?

1/R = 1/6.25 + 1/7.5

Also, can you list step by step on how you figured this out?

Thanks a ton :thumbup:
get rid of denominators.

6.25*1/R = 6.25*1/6.25+ 6.25*1/7.5

6.25/R= 1 + 6.25/7.5

7.5*6.25/R = 7.5 + 7.5*6.25/7.5

7.5*6.25/R = 7.5 + 6.25

7.5*6.25*R/R = (7.5+6.25)*R
7.5*6.25 = 13.75R

7.5*6.25/13.75 = R

#### Tsmil

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five.five-six said:
Dennis doesn't use a calculator, Dennis is a calculator!
I meant that for the OP. He has the right formula, was just wondering if he didn't know how to punch it in correctly.

#### bigbenny

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##### Registered
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4 Posts
Discussion Starter · ·
Thanks guys awesome work. 3.41 is correct.

Sent from my DROID RAZR using Tapatalk

#### don_resqcapt19

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get rid of denominators.

6.25*1/R = 6.25*1/6.25+ 6.25*1/7.5

6.25/R= 1 + 6.25/7.5

7.5*6.25/R = 7.5 + 7.5*6.25/7.5

7.5*6.25/R = 7.5 + 6.25

7.5*6.25*R/R = (7.5+6.25)*R
7.5*6.25 = 13.75R

7.5*6.25/13.75 = R
That sure looks like a lot of key strokes to get the answer when all you have to do is add the reciprocals of all of the resistors that are in parallel and then take the reciprocal of the sum.

#### chewy

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##### Data Tech/Apprentice.
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9,013 Posts
Parralel is just X^-1 + X^-1 on a calculator.

#### rewire

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get rid of denominators.

6.25*1/R = 6.25*1/6.25+ 6.25*1/7.5

6.25/R= 1 + 6.25/7.5

7.5*6.25/R = 7.5 + 7.5*6.25/7.5

7.5*6.25/R = 7.5 + 6.25

7.5*6.25*R/R = (7.5+6.25)*R
7.5*6.25 = 13.75R

7.5*6.25/13.75 = R
common core

#### don_resqcapt19

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Parralel is just X^-1 + X^-1 on a calculator.
That works too, but still more keystrokes than using the reciprocal key. 3 key strokes to raise X to the -1 power and only one using the reciprocal key to get the same result.

#### chewy

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##### Data Tech/Apprentice.
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9,013 Posts
That works too, but still more keystrokes than using the reciprocal key. 3 key strokes to raise X to the -1 power and only one using the reciprocal key to get the same result.
Thats the only way I know from being taught at night school.

#### don_resqcapt19

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Thats the only way I know from being taught at night school.
Most calculators that have a X^y key also have the reciprocal (1/x) key.

For the problem in this thread, enter 6.25, then hit 1/x, then hit +, then enter 7.5, then hit 1/x, then hit =, then hit 1/x and you have your answer.

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