Question

The 10th term of an arithmetic series is 34, and the sum of the first 20 terms is 710. Determine the 25th term.

Answer 1

S(10) = a + (n-1)d
    34 = a + 9d ---- Eqn 1
 Sum(20) = n/2(2a +(n-1)d)
       710 = 20/2(2a + 19d) ----- Eqn 2
Solve these two equations and find the value of a and d and put the values in the first eqn (a + (n-1)d) to find the 25th term    
*n = the term
*a = the starting number 
*d = the difference in the series for each number