Question

if the sum of the first 60 positive integers is s, what is the sum of the first 120 integers in terms of s? a. 2s 3600 b. s^2 3600 c. s^2 - 3600 d. s 3600

Answer 1

For the first 60 positive integers, a = 1, n = 60, l = 60.
Sn = n/2(a + l)
s = 60/2(1 + 60) = 30(61)

For the next 60 positive integer, a = 61, n = 60, l = 120
Sum = 60/2(61 + 120) = 30(61 + 120) = 30(61) + 30(120) = s + 3600

Sum of first 120 positive integers = s + s + 3600 = 2s + 3600