I posted a question last night but all that happened was I became even more confused.

The homework question is:

Find the sum of each geometric series.
a) S10 in the series $2500 +$2562.50 + $2626.56 + ... now i would normally use the formula tn= ar^n-1 except I do not know what tn equals. To find the ^n I need to know what tn is. Now can some one please help me. 2. Hello, VDestinV! Find the sum of the geometric series. a)$\displaystyle S_{10}$in the series: .$\displaystyle \$2500 + \$2562.50 + \$2626.56 + \hdots$
First, find the common ratio $\displaystyle r.$

We have: .$\displaystyle \frac{2562.50}{2500} \:=\:1.025$

. . . .and: .$\displaystyle \frac{2626.56}{2562.50} \:=\:1.024999024$

The common ratio appears to be: .$\displaystyle r \:=\:1.025$

Then: .$\displaystyle S_{10} \;=\;2500\,\frac{1.1025^{10}-1}{1.025-1} \;=\;128,008.4544 \:\approx\:\$128,008.45 $3. Originally Posted by Soroban Hello, VDestinV! First, find the common ratio$\displaystyle r.$We have: .$\displaystyle \frac{2562.50}{2500} \:=\:1.025$. . . .and: .$\displaystyle \frac{2626.56}{2562.50} \:=\:1.024999024$The common ratio appears to be: .$\displaystyle r \:=\:1.025$Then: .$\displaystyle S_{10} \;=\;2500\,\frac{1.1025^{10}-1}{1.025-1} \;=\;128,008.4544 \:\approx\:\$128,008.45$
wow thanks... but uhh what about the n?

4. 10 is n, as I explained in the other thread.

5. Originally Posted by Soroban
Hello, VDestinV!

First, find the common ratio $\displaystyle r.$

We have: .$\displaystyle \frac{2562.50}{2500} \:=\:1.025$

. . . .and: .$\displaystyle \frac{2626.56}{2562.50} \:=\:1.024999024$

The common ratio appears to be: .$\displaystyle r \:=\:1.025$

Then: .$\displaystyle S_{10} \;=\;2500\,\frac{1.1025^{10}-1}{1.025-1} \;=\;128,008.4544 \:\approx\:\$128,008.45 $I was looking over your calculations... shouldn't .$\displaystyle S_{10} \;=\;2500\,\frac{1.1025^{10}-1}{1.025-1} \;=\;128,008.4544 \:\approx\:\$128,008.45$

actually be .$\displaystyle S_{10} \;=\;2500\,\frac{1.025^{10}-1}{1.025-1} \;=\;28,008.4544 \:\approx\:\$28,008.45 $6. Yes, that's correct. 7. okay but i tried to do that with this one but it didnt work s12 in the series 60, 12, 2.4, ... 8. Originally Posted by VDestinV okay but i tried to do that with this one but it didnt work s12 in the series 60, 12, 2.4, ...$\displaystyle a = 60\displaystyle r = \frac{12}{60} = 0.2\displaystyle n = 12\displaystyle S_{12} = \frac{60(1 - 0.2^{12})}{1 - 0.2}\displaystyle S_{12} = 75\$