First of all I am Muslim as many know here. I do not think that certain things you can gauge in numbers or %age. I personally believe 100% that there is God. However I do not believe in tooth fairy, Santa, and all other things people talk about here. But as I said, someone will ask me that where is the proof for me to be 100% certain. So what would I do? Nothing much being a human. Because as human our knowledge as well as abilities are very limited does not matter how clever we think we are, there would still be so many things around you that you would not have any idea about. How much your wife, son, daughter, husband or other relatives love you, or hate you. can you put that in %age? Or can you even prove that with 100% surety?
We human totally depend on our given senses. Someone shows a picture of Australia to jake and he would believe in it. But perhaps that person showed him picture of Afghanistan and said it was Australia. How would Jake know? So Jake is totally dependent on the reputation of that other person. I have a simple (if understood) or difficult (if not understood) reason to believe in God. A human has nose, eyes, ears, hands, tongue etc to tell something exists or not. But there are so many things that do not exist according to these tools. Do your thoughts exist? How would you prove? When a person is dead he still has eyes, ears, nose etc. What is missing that he does not listen, move or speak any more? Can you prove what that was which is missing now? What would you call it? We did not see it, but something was there which is there no more.
So all of us believe in someone else. Few believe in what few prophets said and few believe in what few scientists said. Difference lies in time. Few believe it as Faith and few as scientific fact (or even theory sometimes). Science still has long way to go to prove few things. But I am sure one day they will. But for few that might be too late.