Question

Calculate S5 for the sequence defined by {an}={1+5/2n} 13.5 23 40 42.5

Answer 1

This is an arithmetic series, where S5 means the sum of the first 5 numbers in the series. The general formula is:

Sn = (n/2)(a1 + an)

So,
a1 = 1 + 5/2(1) = 3.5
a5 = 1 + 5/2(5) = 1.5

S5 = (5/2)(3.5+1.5)
S5 = 12.5

The answer should be 12.5