I'm stuck on this math problem: A teacher uses a 5-inch piece of chalk to write math equations on a chalkboard for his students. The teacher likes to conserve chalk, so he tries to only use 20% of the chalk each day. Since the teacher cannot write with a very small piece of chalk, he recycles the chalk when it is smaller than 2 inches. On Monday the teacher used a new piece of chalk. His students need extra help that day, so he ended up writing more than usual. He used up 45% of the chalk by the end of the day. If the teacher goes back to using only 20% of the chalk each day, how many days does he have before he has to recycle this piece?
Can you help?