QUESTION RELATED TO CRAWLING?

My 8 mth old has been getting up on her knees rocking for about two weeks now wondering what everyone elses experiences are like how long from when bubbys start rocking did they actually crawl i know every bub is different but just a guideline to when she will start crawling and some advice on what i can do to encourage her i put toys in front of her but just out of reach and tantrums start being thrown lol she hates it