+121 The first term of an arithmetic sequence is 2. The sum of the third and the sixth terms is 25. What is the fourth term?
+48 An arithmetic sequence has a common difference between each term
Let the common difference be n
The first term = 2
The second term = 2+n
The third term = 2+2n
The fourth term = 2+3n
The fifth term = 2+4n
The sixth term = 2+5n
And so on...
The sum of the third and sixth terms is 25 so:
2+2n+2+5n = 25
7n+4 = 25
7n = 21
n = 3
Thus, the fourth term is 2+3n = 2+9 = 11
