To round 3.9011639239 to the nearest thousandth, follow these steps:
Identify the thousandth place: In the number 3.9011639239, the thousandth place is the third digit after the decimal point, which is 1.
Look at the ten-thousandth place: The digit in the ten-thousandth place (the fourth digit after the decimal point) is 1.
Apply rounding rules: Since the digit in the ten-thousandth place (1) is less than 5, you do not change the thousandth place.
Final rounded result: The thousandth place (1) remain same 1, so the number rounds to 3.901
Thus, 3.9011639239 rounded to the nearest thousandth is 3.901