Question: What is the sum of the first 6 terms of the arithmetic progression 1, 4, 7, ...?
Options:
Correct Answer: 45
Solution:
The first term a = 1, common difference d = 3. The sum of the first n terms S_n = n/2 * (2a + (n-1)d). For n = 6, S_6 = 6/2 * (2*1 + 5*3) = 3 * (2 + 15) = 3 * 17 = 51.