Gabriel wrote his name $$100$$ times in the sand. What was the $$100\text{th}$$ letter he wrote? ． 
Overseas Competition->Knowledge Point->Word Problem Modules->Periodic Problems->Periodic Problems of Basic Permutation
The $$1\text{st}$$ letter Gabriel wrote was $$G$$, and every $$7\text{th}$$ letter after was $$G$$.  The $$99\text{th}$$ letter he wrote was $$G$$, and the $$100\text{th}$$ was an"$$a$$." 