Danny read $$20$$ pages of a storybook on the first day. On the second day, the number of pages he read increased by $$5$$. The number of pages he read on the third day was $$5$$ more than that of the second day, and so on. If he read the remaining $$80$$ pages of the storybook on the last day, how many pages were there in the storybook? 
Overseas Competition->Knowledge Point->Word Problem Modules->Practical Application of Arithmetic Progression