To round the decimal number 8.59973 to the nearest thousandth, we need to focus on the digit in the thousandths place and the digit immediately following it.
In the number 8.59973, the digit in the thousandths place is 9 (which is the third digit to the right of the decimal point), and the digit immediately following it is 7 (the fourth digit to the right of the decimal point).
The rule for rounding is straightforward: if the digit after the place you are rounding to (in this case, the digit in the ten-thousandths place) is 5 or greater, you round up. If it’s less than 5, you round down.
Since the digit 7 is greater than 5, we round the 9 in the thousandths place up by 1, which gives us 10. However, since this exceeds 9, we need to carry over to the left, adding 1 to the preceding digit (the hundredths place), turning 9 into 10, effectively increasing the whole number.
Thus, rounding 8.59973 to the nearest thousandth results in:
8.600