Wednesday

November 25, 2015
Posted by **Riana** on Tuesday, January 1, 2013 at 11:34pm.

- math help! -
**drwls**, Wednesday, January 2, 2013 at 10:06amLet a = first term, T1

Let b = Tn+1 - Tn = term difference

a + 9b = 34

S20 = T1 + T2 + ...T19 + T20

= a + (a+b) + (a+2b) + ...(1+19b)

20a + (b)(1+2+3+...19)

= 20 a + 190 b = 710

20a + 180b = 680

10 b = 30

b = 3

a = 34 -27 = 7

Arithmetic Series is

7, 10, 13, 16, 19, 22, 25, 28, 31, 34,...

10th term = 34

Check the sum of the first 20 terms and predict the 25th