# Quick question about a book example

Discussion in 'Homework Help' started by torx11, Nov 4, 2013.

1. ### torx11 Thread Starter New Member

Oct 6, 2011
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0
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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Last edited: Nov 4, 2013
2. ### MrChips Moderator

Oct 2, 2009
12,652
3,461
So the discrepancy is 10Ω or 0.05%. Don't worry about it.

3. ### torx11 Thread Starter New Member

Oct 6, 2011
13
0
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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4. ### Jony130 AAC Fanatic!

Feb 17, 2009
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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 ?

5. ### torx11 Thread Starter New Member

Oct 6, 2011
13
0
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.

6. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,993
1,116
Don't worry too much about it. Error in printing can happen.

torx11 likes this.
7. ### torx11 Thread Starter New Member

Oct 6, 2011
13
0
I hope that is the case. Thanks for your time.