The local baseball team is advertising a special deal on ticket prices. The cost of the first ticket to a game is $12 and every ticket after that costs $0.25 less. If the maximum number of tickets you can buy is 30, what is the total cost of 30 tickets?

Question

Wouldn't you use

Sn = n / 2 (a1 + an)

Answer 1

So you are finding
12 + 11.75 + 11.50 + ... for 30 terms

I would use
S(n) = n/2( 2a + (n-1)d) since we don't know the last term, as needed in your formula
I know we could find the last term, then use your formula but the above one would be faster in this case

S(30) = (30/2)(24 + 29(-.25))
= 15(16.75) = 251.25