In order to round a number to the nearest thousandths, we have to check the number in the ten thousandths place:
1- If the number in the ten thousandths is less than 5, then the thousandths number will remain the same and all numbers after it will be converted to zeroes.
2- If the number in the ten thousandths is equal to or greater than 5, then the thousandths number will be incremented by 1 and all numbers after it will be converted to zeroes.
Applying this to the given number:
1.80431
The number in the ten thousandths position is 3 which is less than 5.
Therefore, rounding 1.80431 to the nearest thousandths will be:
1.80400 which is equivalent to 1.804
