The set consisting of only -9 ie {-9},
the set consisting of -9 and 5 = {-9,5},
the set consisting of -9 and 3 and sqrt(17) = {-9,3,sqrt(17)}, and so on.
Natural numbers.
1.18 is a number and number do not contain any sets (of any kind).
-10 belongs to the set of all integers denoted by Z.
173 belongs to the set of positive natural numbers and it also belongs to the set of prime numbers.
19 doesn't belong. The rest of the numbers are multiples of 3.
Rational numbers
real numbers, irrational numbers, ...
Natural numbers.
It can be element of: Rational numbers or Real numbers
17 belongs to the set of prime numbers
1.18 is a number and number do not contain any sets (of any kind).
Irrational Numbers which are a subset of Real Numbers which are a subset of Complex Numbers ...
numbers
The LCM of 3 and 9 is 9.
The rational numbers, the real numbers and sets of higher order which contain the reals such as the complex numbers.
-10 belongs to the set of all integers denoted by Z.
Infinitely many sets: they belong to the set {0, 2, 4, 5, 7, 9}, and to {0, 2, 4, 5, 7, 9, 92} and {0, 2, 3, 4, 5, 7, 9} and {0, 2, 4, 5, 5.35, 7, 9} and {0, 2, 4, 5, 7, sqrt(53), 9} and N0, the set of Natural number including 0, Z, the set of integers, Q, the set of rational numbers, R, the set of real numbers, C, the set of complex numbers as well as any superset of these sets.