I tried to solve this, but I am unsure about my solution. I'm posting it here to see if I got it right. It is listed as multiple choice, but I am unsure about the quality of the puzzle creator, so don't limit yourself to the 5 provided answers.
A gardener wants to plant 100 trees (oaks and birches) alongside a trail in a park. The number of trees between any two oaks must not be equal to five. What is the largest number of oaks that the gardener could plant?
Planted in a pattern like this (O=Oaks, X = Birches), repeating to 100.
I'm quite certain there is a better way to solve this (and a better answer), so enlighten me on how to solve a problem like this.