# CFA Level I Question

How would you solve this algebraically? Can you show your work? Thanks!

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Multiply every term by (1 +

r)^{2}. You’ll get a quadratic equation for which you can use the quadratic formula.Simplify the complicated side; don't complify the simplicated side.

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I get 8.53266% using the CF worksheet. Nothing wrong with the quadratic formula, but if I treat this as cash outflows of -10 at time 0 and -100 at time 1 to get an accumulated value of $120.312, the IRR function saves oodles of time!!!

“Mmmmmm, something…” - H. Simpson

But you didn’t get -120.853%.

Simplify the complicated side; don't complify the simplicated side.

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I don’t see quadratics in the CBoK, Coach!!!

“Mmmmmm, something…” - H. Simpson

Nor do I.

I was answering a question specifically asked about algebra.

Simplify the complicated side; don't complify the simplicated side.

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Studying With

still a better love story than Twilight.

¯\_(ツ)_/¯ It be like that sometimes.

Step 1: Multiply by (1+r)2 (thats squared, I cannot write it properly on here, sorry) as proposed by S2000magician

Step 2: You now have 10r2 + 120r + 110 = 120.31 which can be written as 10(r2 + 12r + 11) = 10(12.03)

Step 3: Divide by 10 to get r2 + 12r + 11 = 12.03 We have a quadratic equation here. To solve algebraically, you need ot turn it to a true quadratic equation. We do it by adding 25 to both sides of the equation so equilibrium holds - r2 + 12r + 36 = 37.03

Step 4: Transform left side to (r+6)2 and apply a SQRT to both sides

r + 6 = 6.085

r = 0.085 or 8.5%

This is close to a IRR calculation which is done by trial and error, its just that Excel or the TI calculator are fast at it (and the TI calculator is annoyingly slow when you want to be fast with it). If you cannot convert to an equation that can be solved, you have to put some value for r and see where the equation goes. Then another and after some trial and error you`d get to the actual result, or very close to it.

Sure you can: we have superscripts in the ribbon, above.

(1+r)

^{2}Simplify the complicated side; don't complify the simplicated side.

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Newton-Raphson or hacksaw!!!!

“Mmmmmm, something…” - H. Simpson