An arithmetic progression has first term 11 and fourth term 32. The sum of the first nine terms is
The correct answer is A. 351
The first term (a) of the arithmetic progression (AP) is 11 and the fourth term is 32.
In an AP, the nth term is given by a + (n-1)d, where d is the common difference.
So, we can write:
a + 3d = 32
Given that a = 11, we can substitute this into the equation to find d:
11 + 3d = 32
3d = 32 - 11
3d = 21
d = 21 / 3
d = 7
The sum S of the first n terms of an AP is given by the formula:
S = n/2 * (2a + (n-1)d)
Substituting n = 9 (since we want the sum of the first nine terms), a = 11, and d = 7 into this formula gives:
S = 9/2 * (2*11 + (9-1)*7)
S = 9/2 * (22 + 56)
S = 9/2 * 78
S = 351