math
posted by Annie on .
the 10th term of an arithmetic series is 34, and the sum of the first 20 terms is 710, determine the 25th term.

I will assume that you know the formulas for term(n) and sum(n) of an AS
10 term is 34 > a+9d = 34
sum of 20 terms is 710 > (20/2)[2a + 19d] = 710
2a + 19d = 71
double the first equation, then subract
2a + 18d = 68
d = 3
back into 1st > a + 27 = 34
a = 7
term(25) = a+24d = 7 + 72 = 79 
Thanks :) so much

uidont