An arithmetic series has first term -50 and common difference 4. How many terms are in the series so that the sum of the series first exceeds 100?

Answer 1

Again, use your definition.

you know S(n) = (n/2)(2a + (n-1)d ), so

(n/2)(2a + (n-1)d ) > 100

and you know both a and d

remember that n has to be a whole number, and you will end up with a quadratic inequality.
(n/2)(2a + (n-1)d ) = 100 ,
sub in your values, solve the resulting quadratic for n
round up your n to the next whole number