When to use these formulas?

ssy · Posted: Mon Oct 22, 2007 3:17 am Post subject: When to use these formulas?

I've just seen these formulas on the "Quant revision" notes downloaded from the GMAT wiki.

Can someone please explain what they mean and when they should be used? I've gone through all questions in the OG guide and do not seem to have needed to use any of these formulas.

What do the variables "a", "r" and "n" in the equations stand for? Thanks!

AP: An = a + (n-1)d
Sn= n/2[2a+(n-1)d]

GP: An= a[r^(n-1)]
Sn= a[(r^n)-1]/r-1

Sum of squares of 1st n natural numbers: n(n+1)(2n+2)/6

Sum of cubes of 1st n natural numbers: [n(n+1)/2]^2

jangojess · Posted: Mon Oct 22, 2007 7:12 am Post subject:

Check this link for some explanation....
http://rbmix.com/math/progressions/seq.html

Check this link for some pblms...
http://questionbank.4gmat.com/mba_prep_sample_questions/ap_gp/

achandwa · Posted: Mon Oct 22, 2007 6:38 pm Post subject:

thanks for the links jangojess!
-Ashish

ssy · Posted: Tue Oct 23, 2007 7:23 am Post subject:

Yes JangoJess these links are immensely helpful, a thousand thanks.