Who, What, When, Where, Why, God, Why?
According to polls (such as Gallup, which record how people think about God). If a majority of people believe it, then it must be true.
Truth is relative. It all depends on your point-of-view.
According to the Scriptures: God chose to reveal Himself through His work of creation (generally, invisible attributes) and also through intervention (special times and places where He revealed His existence to His people of old, such as Moses) and later when He became a man, Jesus.
It is impossible to know if God exists. He never has done anything to reveal himself plainly.
1 in 10, not too many.
3 in 10, a small number.
6 in 10, a little more than half of all people living in North America.
Still more than 9 out of 10 for over the 6.5 decades that the question has been repeatedly asked.
Yes, radically different. One is primarily loving and gracious while the other is more punishing and demanding.
No, they are exactly the same God, but in the New Testament He appears in, through, and as, the man Jesus.
The uncanny fulfillment of Messianic prophecy
The reports of the healings and miracles he performed
His wisdom and teachings about the Kingdom of God
Multiple eye-witnesses who saw Jesus physically resurrected from the dead (St. Paul says "more than 500 people" witnessed, 1 Corinthians 15)
Simply that he died and rose and nothing more.
The cross and resurrection are meant to reveal that God truly loves us, see John 3:12-18.
It means that we have been reconciled back to God (2 Corinthians 5:15, 19).
It is meant to reveal that God is too busy to do anything about the problem of sin and death. Please leave Him alone.