Answer:
0.009
Explanation:
We have been given a decimal number 0.0091. We are asked to round our given number of nearest thousandth.
Rounding to nearest thousandth means to round to three places after decimal.
We can see that fourth digit after decimal is less than 5, so we will round 3rd digit after decimal to 9.

Therefore, our given number rounded to the thousandths would be 0.009.