1. Can I use American English in the IELTS test?
Yes. Examiners just want to hear good, clear English, wherever it's from.
2. What is the difference between "a number of" and "the number of"?
There are many grammar websites on the Internet that explain this kind of thing. Click here to see one that I found just now.
3. Do you have an ebook for writing task 1?
No. I try to cover everything you need to know for task 1 in the lessons here on the blog. I'm hoping to produce some video lessons for September, so I'll teach writing task 1 in a more organised way then.
4. How can I achieve a band 7?
I'm afraid there isn't a simple answer to that question. Hopefully I'm gradually answering it in the daily lessons that I write. Keep studying hard and the secret will reveal itself!
5. In the listening test, if the question asks "where can you buy a ticket?", do we need to write "at the post office" or just "post office"?
The short answer "post office" will be fine. They just want the key words.