We have already gone over how the Bible in one place says God tempts David and in another Satan tempts David to take the census. And as Ben Kenobi says, "So what I told you was true, from a certain point of view."
So what about the difference in numbers?
2 Samuel 24:9
And Joab gave up the sum of the number of the people unto the
king; and there were in Israel eight hundred thousand valiant
men that drew the sword; and the men of Judah five hundred thousand men.
1 Chronicles 21:5
And Joab gave the sum of the number of the people unto David.
And all they of Israel were a thousand thousand and a hundred
thousand [1,100,000] men that drew sword; and Judah was four
hundred three score and ten thousand [470,000] men that drew the
sword.
And we know that it is true because it makes sense for a bronze age tribe to have a million and a half men in the army. That is larger than the active US Military but the Bible is accurate. Too bad there is no archaeological evidence to back that up. Oh yeah, God destroyed all evidence of that to test our faith.