Mathematicians handle uncertainty using probability theory, Dempster-Shafer theory, fuzzy logic. See also probability.
Examples where uncertainty is important:
Further Reading
... family size is 3.51. In the town the population is spread out with 29.5% under the age of 18, 6.7% from 18 to 24, 33.6% from 25 to 44, 20.6% from 45 to 64, and 9.6% ...