I read 1/5 on the first day, which is 300* 1/5=60 pages.
Read the remaining 25% the next day, that is, (300-60)*25%=60 pages.
You can ask questions like this:
First question: How many pages did you read on the first day?
Answer: 300* 1/5=60 pages.
Second question: How many pages did you read the next day?
A: (300-60)*25%=60 pages.
You can also ask this question:
First question: How many pages have you read?
A: 60+60= 120 pages.
Second question: How many pages are left?
A: 300-60-60= 180 pages.