# yes another one....

• Nov 2nd 2008, 02:55 AM
pop_91
yes another one....
the sum of the first ten terms of an arithemetic series is 50, and the sum of the first twenty terms is 180. find the common difference and the first term of the series.

ok this is not going well.... thanks for any help
• Nov 2nd 2008, 03:07 AM
mr fantastic
Quote:

Originally Posted by pop_91
the sum of the first ten terms of an arithemetic series is 50, and the sum of the first twenty terms is 180. find the common difference and the first term of the series.

ok this is not going well.... thanks for any help

This is straightforward application of the formulae:

$50 = \frac{10(a + 9d)}{2}$ .... (1)

$180 = \frac{20(a + 19d)}{2}$ .... (2)

Simplify equations (1) and (2) and then solve them simultaneously.
• Nov 2nd 2008, 03:09 AM
pop_91
ooooooooooh i didnt think of doing that!

thank you