Grandpa is writing a book. Every morning he starts writing vigorously and fills a lot of pages. But post-lunch he goes through all that he's written that far (right from day one) and deletes one-fifth of it. He doesn't write anything more that day. At the end of the day the content of his book is still $20\%$ more than that at the end of the previous day.
How much percent new content does Grandpa write in the morning?