Writing new code vs. re-writing someone else's code

Hello, This question could be seen as a general programming question, but because PHP is what I know best, I'll ask it here. A good friend of mine is the person who got me more interested in programming as a career. She's a professional COBOL programmer, and works for a large bank. She once told me that 75% of her time was spent going over and rewriting/repairing old code that she didn't write, and only 25% writing new code. From what I know about COBOL, it seems that it might need more rewriting than other languages, because of all the built up old code. But as I look forward to the day when I can work as a full-time PHP coder, I wonder. The question is, how much of your time (you, the professional PHP coder reading this), is spent rewriting/repairing old code vs. writing new code. Although this is a PHP list, and my question is in regards to PHP, if you want to give me your opinion on this same question in regards to other languages you've programmed in, I wouldn't mind. thanks, William