1. ## 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

2. 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.

3. ooooooooooh i didnt think of doing that!

thank you