Question

Write the series in summation notation:

100 + 95 + 90 + 85 + 80

Answer 1

you are starting at 100 and decreasing by 5 each time

so the basic nth term formula is

an = a1 + d(n-1)

an = 100 + (-5)(n-1)

an = 100 - 5n + 5

an = -5n + 105

Answer 2

then you are adding up the first 5 terms, which means you would write out