# Quick question about a book example

#### torx11

Joined Oct 6, 2011
13
I need help finding out how did the authors got the values R1 = 30.45kΩ and R2 = 19.55kΩ.

When I for solve for R1 and R2 I get the following values:
R1 = 30.440kΩ
R2 = 19.560kΩ

Equation I used was:
R2*(2.5V)/(50000Ω) = 0.978V

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#### MrChips

Joined Oct 2, 2009
31,087
So the discrepancy is 10Ω or 0.05%. Don't worry about it.

#### torx11

Joined Oct 6, 2011
13
Thank you for your prompt assistance. But surely this discrepancy can't be correct because if you check the continuing example in the attachment, you would see the authors get an R1 = 1.45kΩ and R2 = 3.55kΩ.

If I calculate using the same equation as before but now with 5kΩ I would get R1 = 2.556kΩ and R2 = 2.444kΩ.

Equation I used was:
R2*(2.5V)/(5000Ω) = 1.278V

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#### Jony130

Joined Feb 17, 2009
5,539
For Vx = 1.278V and R1 +R2 = 5K the correct solution is R1 -> 2.444K R2 -> 2.556k
But can you buy 2.444K or 2.556 resistor ?

#### torx11

Joined Oct 6, 2011
13
Thanks for your input Jony130. That is the value I got but apparently the authors got different R1 and R2 values for both of these examples. The first example differed only slightly while the second example is by a landslide.

#### Jony130

Joined Feb 17, 2009
5,539
Don't worry too much about it. Error in printing can happen.