Prayer is answered by belief.
So if you know that God can, then He will.
When mine are answered, nothing this side of Earth could have done the same.
Example, 2 years ago I had a car that would not pass rego, and a friend who's mother had just died said to me''would you like my mothers car''.
I asked her 'why' was she asking me, and she told me God had told her that I was the person who would look after her mothers car.
So she gave me this $5,000 car ! but it gets better, it was the exact same colour as my old car, and takes only half the petrol.
I had been saying for months how I didn't know how much longer I could put in $100 of petrol per week.Now it is exactly $50!
That's only one answer to prayer, but when it is from God you know, because it is exactly what you need.Or even more!
I'm not sure. Sometimes it can take years and other times you will never know. When I was in the second grade, I used to pray for my mother to stop smoking. She stopped smoking about the time I finished school.
Seriously though, if the answer was "no", you wouldn't know. If it's a yes, well, people's stories about that tend to look like random chance or coincidence to me, so I suppose it's up to the individual to decide when they think they've gotten an answer.