Quist Quiz Solution

QuistQuizMay1959

 

Yesterday, we presented the problem shown above and promised that we would show the solution today.  The problem isn’t particularly difficult, and there are probably other ways to do it.

Since 15 volts is measured across the 30K resistor (and R2), this means that 30 volts is dropped across R1, which happens to be twice as much as 15.  This means that R1 is twice as large as the combined parallel resistors.  Since only the ratio is important, it’s easier to work in kilohms rather than ohms:

R1 = 2 (30 R2 / (30 + R2))

We’re also told that R1 + R2 = 15.

They might look a bit messy, but we now have two equations and two unknowns, meaning that we can solve them.  In my scribbling below, I used the variables X and Y to keep things a bit more legible.

After crunching the numbers (including use of the dreaded quadratic formula), we arrive at the answer:

R1 = 9416 ohms, and R2 = 5584 ohms,  [See the comment from eagle-eyed K3CHJ who caught my earlier typo!]

the same answer given in the June issue.  So when you asked your poor sainted algebra teacher, “when will we ever have to use this in the real world?,” he or she should have pointed out that you might need it someday for your blog.

ResistorProblem

 




 

One thought on “Quist Quiz Solution

  1. Jim Toth, K3CHJ

    You blew it at the last step, your answers add up to 15.1k. R1 is 9416 ohms.

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