find the sum of the first fifty terms of the arithmetic series: 11.4+9.1+6.8
The 50th term is found by : 11.4 - 2.3(50-1) = -101.3
And the sum is given by : (Number of terms)* [ 50th term + 1st term] / 2 = 50 * [ -101.3 + 11.4] / 2 = -2247.5
