The number 1.68 belongs to the following set(s) of numbers:
- Rational numbers: Because it can be expressed as a fraction (for example, 1.68 = 168/100).
It does not belong to the following sets:
- Natural numbers: These are positive integers (1, 2, 3, ...), and 1.68 is not a whole number.
- Whole numbers: These include all natural numbers and zero (0, 1, 2, 3, ...), and 1.68 is not a whole number.
- Integers: These are whole numbers that can be positive, negative, or zero (..., -2, -1, 0, 1, 2, ...), and 1.68 is not an integer.
- Irrational numbers: These cannot be expressed as a fraction of two integers, but 1.68 can be expressed as a fraction.
So the correct answer is: rational numbers.