Posted by **Courtney** on Tuesday, September 28, 2010 at 7:00pm.

11,406.14=(438.3/r)(1+r)^10 how do you solve for r?

- calculus -
**Reiny**, Tuesday, September 28, 2010 at 8:25pm
These are very "nasty" equations, since there is no simple-level method of solving these.

I reduced it to

(1+r)^10 = 26.02359r

If you know Calculus, you can use Newton's Method,

otherwise, try something like this

It looks like your equation could have come from the amount of an annuity formula, so the r is probably an interest rate

make a chart with 3 columns

r | Left Side|Rigth Side

.05 1.62889 1.3 ---- off quite a bit

.06 1.79084 1.5614 --- let's go higher

.09 2.36736 2.345 --- hey, not bad

.095 2.4782 2.47224 -- closer !!

.096 2.50095 2.49826

.097 2.523866 2.524288 notice the Right side is now > the left side

so our r must be between .096 and .097

try .0965

Do you get the idea?

With a good calculator and some calculator skills this is not so bad

BTW, I put 26.02359 into memory of calculator

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