Here’s a question from the May 2023 (US) SAT, non-calculator section:

Alice took 60 minutes to complete a task on her first trial. The time it took Alice to complete the task decreased by 10% of the previous time for each additional trial. Approximately how many minutes will it take Alice to complete the task on her fifth trial?

A) 50

B) 42

C) 39

D) 35

I know we can solve this by subtracting 10% of the current value 5 times, but is there a more direct way to solve, maybe as a function?