Question

For an arithmetic sequence where a1 = 17 and the common difference is 5, find s7.

A. 219
B. 229
C. 224
D. 235

Answer 1

The correct answer is C. 224

Further details:

Using the formula for calculating the sum of an arithmetic sequence


`S_(n) = (n)/(2) (2*a_(1) +d(n-1)) \\ S_(7) = (7)/(2) (2*17+5(7-1)) \\ S_(7)=(7)/(2) (34+30) \\ S_(7)=(7)/(2) (64) \\ S_(7)=(7*64)/(2) \\ S_(7)=(7*32)/(1) \\ S_(7)=224`